How many 1st class stamps to use on heavy letters?

In our office, we buy Royal Mail stamps in ready to use denominations of “1st Class”, “2nd Class”, “Large 1st Class” and “Large 2nd Class”. However, these are only useful for 100g weight letters.

For heavy letters, we can use multiples of these stamps. I noticed I was routinely having to do the calculation in my head as to what is the optimum combination of stamps. For example, what to stick on a 500g 2nd class large letter. I know that’s £1.58, I know the stamps represent the 100g values, so 1st=65p 2nd=56p Large_1st=98p and Large_2nd=76p.

It’s not too hard to work out, but it takes time and gets harder with bigger letters and parcels.

For a coding challenge, I wrote “Stampulator“. It’s a single web page that tells us which combinations of stamps to use, so for the 500g 2nd Class large letter, £1.58 example, we need 1 x 1st class and 1x Large 1st class. That’s over by 5p, but it’s the nearest value to the cost.

I also made it so that if I have different value stamps or a different target value to reach (say; special offer or I’ve been slow to update the values when Royal Mail prices change) I can input those and get an instant result.

I then printed the page and stuck it buy our post box.  Stampulator is on my web server and free to use – it works well from a mobile phone too.

Post a comment here if it’s useful and that’ll encourage me to keep it up to date.


52 responses to “How many 1st class stamps to use on heavy letters?”

  1. reuben mcgowan

    Nice idea, thank you. I’ve found it helpful

  2. Hello,

    I have a question.
    Can I use for exapmle 2x RED LARGE STAMPS for a large letter ( 1st class) up to 500g instead 2x red class and 1x blue class If I will buy cheaper Large stamps let’s say from an ebay?

    Thank you for a stampulator si very helpful.

    1. You can use any combination of stamps that match (or exceed) the required postage value.

      For some values, you can match the required postage with different combinations but stampulator only picks the one match. If there’s interest, I could make it so you can follow a link by the result to see other exact combinations of stamps that match the target value.

      Example: If you have stamp values of 10p and 20p, your target is 40p, you could reach that by having
      [4 x 20p], [2 x 10p + 1 x 20p] or [2 x 20p]. Stampulator will only display one.

  3. Hi, I am very glad that I bumped into your article Steve because I didn’t even realise that we could use traditional stamps on Large Letter and Small Parcels! The ‘Stampulator’ is an excellent coding program and I managed to use it successfully earlier today before I went to the Post Office. I have now bookmarked your website for future use. Thank you.
    Please keep up the great work 🙂

  4. Hi again, your ‘Stampulator’ is fantastic and very helpful. Is there any chance you are working on an update for latest stamp (2019) changes?

    1. Thanks for the prompt, I’ll update it this week 🙂

    2. Updated!

      1. Thank you again Steve for the update 🙂

  5. I want to send a large letter 2nd class. I have 2x2nd standard size [2nd not 61p] and a 10p. Is that OK?

    1. I should add it weighs 125grms and should total £1.32.

      1. Yes, as long as the combination of stamps add up to or exceed the required postage you’re good to go. A “2nd Class” stamp is currently equal to 61p and counted as such, so 2 of those plus a 10p stamp meets the value.

        This also means you can buy a stamp marked “second class” (as opposed to a stamp with a numeric value on it) today for 61p and when the prices go up it will still count as a second class stamp at the new higher value.

  6. Jack Bremer

    Prices have gone up again – are you able to update? Super useful, especially in lockdown. Thanks!

    1. Thanks for the prompt, updated now.

  7. I’ve been waiting for this! And using my own totally unteccie not to mention unsatisfactory excel trial and error version. So helpful thank you. Also still using stamps I bought in bulk 9 years ago. Must have saved a penny or two!

  8. Just stopped by to say that this is really useful, thanks!

  9. Hi Steve, Great calculator but it lacks what I need it for.

    For me I need more stamp options.

    Great for 1st / 2nd class standard and Large sizes.
    Doesn’t work as there is wastage!

    Wouldn’t it be better to under cost the costing rather than over cost?.

    With the under costing I could then add all the extra stamps that I needed.
    Over costing it as you currently have it would mean I will always be a couple of pence in loss.

    Would it be possible that you could add more stamp combinations options?

    As an example my partner is sending a Large letter 2nd class letter to her father with the weight of it being approximately 470 grms.

    I wanted to work out how many stamps that I needed.

    The cost to send is £1.99 because of the weight being 470 grms.

    As I got loads and loads of stamps. Mostly:
    1st Class Standard @ 100grms – £0.85
    1st Class Large @ 100grms – £1.29
    2nd Class Standard @ 100grms – £0.66
    2nd Class Large @ 100grms – £0.96

    Large 2nd Class Letter
    weighing 500grms
    Price: £1.99

    I worked it out with one 1st Class Large stamp costing £1.29
    One 2nd Class standard stamp costing £0.66.
    and then I added two 2pence stamps
    Total: £1.99


    Two 2nd Class Large stampS costing £0.96 = £1.92
    One 5-pence
    One 2-pence
    Total: £1.99

    And so on –

    I hope you understand my examples

    Looking for a calculator that can calculate the highest value downwards without waste.

    Can you do this?

    1. > Wouldn’t it be better to under cost the costing rather than over cost?.
      If your stamp value is less than required, the Royal Mail won’t deliver and will charge the under payment to the receiver along with a handling charge.

      >With the under costing I could then add all the extra stamps that I needed.
      >Over costing it as you currently have it would mean I will always be a couple of pence in loss.
      This is true, we could buy stamps of 1p/5p/10p etc and put the exact postage value on. However;
      * we don’t send very much post,
      * we get the benefit of the ‘1st class’ stamp even once the price has been increased (we buy perhaps £100 of stamps every couple of months)
      * most of the post we do send fits within a multiple of the 1st/2nd/L1st/L2nd stamps
      * If you’re sending lots of packages outside of the standard stamp range, check the royal mail online pricing options. You can buy an exact value stamp/label to print at home. We occasionally use that for tracked post (signed for/special delivery)

      >Would it be possible that you could add more stamp combinations options?
      > Looking for a calculator that can calculate the highest value downwards without waste.

      I think you’ve got enough on the page already. It takes 4 stamp values and you can change them to suit the values you have. You can also set a ‘target’ value in case you need to add signed for, calculate an international postage cost, etc .
      So, change one of the stamps to say, 1p, and you’ll probably get an exact match using up to 36 stamps.

      > As an example my partner is sending a Large letter 2nd class letter to her father with the weight of it > being approximately 470 grms.
      >I wanted to work out how many stamps that I needed.
      >I worked it out with one 1st Class Large stamp costing £1.29
      >One 2nd Class standard stamp costing £0.66.
      >and then I added two 2pence stamps
      >Total: £1.99

      So to use your 2p stamps, replace one of the 4 preset values. EG: I just replaced Stamp4, the “96p Large 2nd” with 2p and it calculated the same combination as you did. There’s often more than one way get an exact match too, quick mental arithmetic suggests 35 x 2p stamps + 1 x large 1st.

      I hope that helps,

  10. I love this, made my job a whole lot easier , I just jump on this website and don’t even need to think doing the maths. Thanks Steve please keep up the good work.

  11. I use this tool all the time for work, it’s really handy as it lives on my bookmark bar.

    Any chance you could update for the new stamp prices please?


    1. Thanks for the prompt, updated for 2022!

  12. Paul MacDonald

    I used Stampulator for the first time today: it’s great!
    Any chance of updating it for the new prices (they went up on 4th April).

    1. Thanks for the prompt, updated for 2022!


    Hi Steve. This is (almost) perfect for me. I inherited a large number of smaller denomination stamps that I’m hoping to use for an ebay clearout, would you be able to update the page to more than 4 stamp prices or is that too big a challenge coding wise?

    1. You can put four of your own values in. So if you have 1p, 2p,5p and 10p the calculator will use the max of 36 stamps for just the standard letter sizes/weights.
      If you only have 3 stamp values, replace the last one with a high number like 999 and it won’t get used in the calculations.

      I could extend to 5 stamp values (or more!) if you can convince me more than 4 denominations is useful 🙂

  14. Great resource for those of us that have bulk bought stamps and now want to use them up! Thank you for sharing it is really appreciated

  15. Hi Steve

    I recently stumbled upon Stampulator, and have found it very useful as I have a stash of 1st Class and 1st Class Large stamps to use up, and have started to sell on eBay – so thank you for this handy webpage.

    I’d like to ask if it would be possible to tweak the code so that amounts below the target value are also returned (but only if the amount to make up is less than the overpayment would be). I see that Saint has already suggested this in an earlier post, but I still think that it is a reasonable suggestion, as the reason you gave for not implementing it is only partially correct (more accurately, it does not necessarily apply in cases where one is sending an item of post at a Post Office counter). Indulge me please, if you will…

    Obviously, if I pop something in the post box with inadequate postage, the recipient will be charged the underpayment plus an additional fee – just as you say. But – and it’s a big ‘but’ – if I send an item in the Post Office, I can apply stamps I already have, then just pay the difference – the counter staff will either apply additional stamps to that value, or somehow indicate on the package that full postage has been paid (I can’t recall how exactly they do this, but the postage label will show the amount paid, regardless of whether I pay in money only, stamps only, or a combination of both).

    Real life example: I have a 130g Large Letter to send 2nd Class (not signed) – cost £1.65. I only have 1st Class and 1st Class Large stamps, so I enter 95 and 145 in the first two boxes, with 9999 in the other two. Stampulator returns 2 x 1st Class stamps (total £1.90, an overpayment of 25p), but I could use 1 x 1st Class Large (£1.45) and pay the extra, which is only 20p.

    The overpayment principle is fine for situations where the sender can’t (or doesn’t want to) go to a Post Office to pay the extra, and is okay with overpaying in stamps. But in my situation (which is hardly unique), it would be very useful to be able to calculate underpayments as well (with the intention of making up the difference at the counter).

    My example isn’t the best one, as there’s only a 5p difference between the underpayment and the overpayment (not to mention that it’s easy in this instance to perform the calculation mentally), so in this particular case one might very justifiably opt to just put two 1st Class stamps on the package, and bung it in the postbox, rather than have to queue up just to save 5p! But of course, there are other scenarios where the difference is greater, and where – from a purely financial perspective – it would be much better to make up the difference in cash (or card payment) rather than overpay in stamps.

    You could argue that the following point isn’t relevant, but I need to obtain a Certificate of Posting for each package I send, so I have to go to the Post Office anyway, even if I have the correct postage, or even if an overpayment in stamps would be a smaller amount than the difference I would need to make up had I applied stamps under the target value. I’m sure that I’m not the only one in this position. So, given that I have to send the packages from the Post Office anyway, having Stampulator calculate underpayments as well as overpayments would make it even more useful.

    A few points to note:

    – I’m aware that the case I’m making for calculating underpayments (as well as overpayments) is only valid from the perspective of somebody sending items at a Post Office counter, where they can pay the difference between pre-applied stamps and the target value; in situations where people are just putting a package in the postbox, it is better that Stampulator only calculates exact payment or overpayment in stamps (as it currently does) – preferable that the sender loses out slightly by overpaying in stamps than the recipient has to pay the shortfall plus a fee on an underpaid item of mail. For this reason, I disagree with Saint’s suggestion that calculating underpayments “rather than” overpayments would be better – ideally Stampulator would do both, but if it’s a choice between the two, then overpayment wins out.

    – Further to the above, I note from your comments that you coded Stampulator based around your own business needs and practices. You have kindly made it publicly available, as it can be of benefit to others, but it meets your needs without the extra function of calculating underpayments – so any work you did to incorporate the ability to calculate underpayments would largely benefit others, rather than your business. I can understand why that would be an inhibiting factor!

    – For all I know (being neither a coder nor particularly great at mental arithmetic), having an underpayment calculation function could result in an unwieldy number of possible permutations being returned. Also, underpayment results are only useful where the underpayment amount is less than the amount of an overpayment (20p vs 25p in my example, but the discrepancy can be far greater in other cases).

    – If I had the requisite mathematical and coding ability, I would happily create the desired program myself. Obviously, it wouldn’t have to be anything to do with stamps per se, just a program that takes user-inputted numerical values (either a single value or a range of them) and shows combinations of them in order of proximity to a target value, below as well as on-target and over-target (with the rules that any number can be used more than once, and not every number has to appear in the combination if a closer result can be attained without it – rules that Stampulator already incorporates). To be honest, I’d have thought that such a tool would be easy to find online, but Stampulator – which does half of the desired job – is ‘all’ (no criticism intended) I’ve come across so far. It doesn’t help that I’m stuck for what to enter as a search term. I’ve looked on the site, but to no avail (it does have a useful Toilet Roll Calculator, though!). Since starting to type this, I’ve spoken to someone who reckons this should be achievable in Excel (or a similar piece of software), but my Excel skills are virtually non-existent through lack of practice.

    At the moment – only sending smaller packages requiring few stamps, and only having two stamp values (1st and 1st Large) to factor in – I can manually calculate the nearest match, but if either (or both) of those variables increases, then the number of permutations to work through quickly rises, as you yourself have remarked.

    Sorry for the long post, but I hope that I’ve made at least a reasonable case for underpayment calculation (although I acknowledge that for your own purposes the program is fine as it is). I’ll continue to use it when sending packages, but as someone who a) already has a stash of stamps, b) wants to watch the pennies, and c) has to send packages from a Post Office in any event (meaning I have that option of paying the difference), I still have to grab pen and paper (and maybe calculator), and work out whether it would be cost me less to underpay in stamps and make the difference up (as opposed to overpaying in stamps).

    1. OK… that took me a while, but there’s now a version that calculates the nearest combination up to the target value –

  16. Catherine

    Thank you for creating the stampulator which I found this morning, by accident. This is very useful as I have several small parcels to send and a mixture of 1st, 2nd, 1st large and 2nd large stamps (without barcodes) to use up before they expire at the end of the month! Although I believe we now have until the end of July, according to Martin Lewis of MSE fame.

  17. Great site, how do you tackle the issue when you have a lot of signed for parcels to post? And all your packages are paid via stamps. My post office is always busy and i have about 20 parcels a day to post.

    1. Can you describe the issue more please?

      If you’ve used the correct signed for prices and put enough stamps on,
      and if you’ve got a stack of signed for labels,
      I would think they’re just scanning them and giving a receipt?

      We don’t post much now but we used to order packs of signed for/special delivery barcode labels, then the postman would collect and sign a receipt book. They send them free to businesses but I would assume the post office will happily give you a bundle if you’re a regular and it speeds things up.

      If you’re sending 20 a day then it’s worth talking to RM as a business (self employed counts as a business). You may be at the point it’s cheaper to run a franking machine (slightly cheaper postage but some fixed costs).

  18. Very helpful to keep track of price changes etc for my discogs and ebay selling activities. The only problem I have is remembering what prices before price increases as I buy plenty of stamps in advance. Your guide tells me what to use but I have to make a separate note of what I actually paid for my stamps to accurately record costs. Even links I save to old RM price pages seem to get updated with the new prices by them. Anyway I find it invaluable. Many thanks.

    1. Tip: Google search “royal mail price guide” (with the speech marks) will help find the PDF version that don’t change. EG: that just returned for me a 2011 price guide that someone saved and shared.

      Thought: you’re describing a common accounting question – how do you value stock? The price you paid? The price it would be to replace today? The price you could get for it if you tried to sell it?

      * If you’re doing it to work out the profit on each job, you can use the today cost because eventually you will replace them at the today cost.
      * If you’re doing it to report your annual profit and thus taxable income, speak to an accountant (they’ll often know of costs or expense you haven’t thought of deducting and lower your tax due) and probably you’ll do either an annual stock valuation if there’s a lot of value there and it becomes treatable as an asset, or it will be a small enough amount to be regarded as a regular expense when bought. In my small business, our stock holding of stamps so small we treat it as an expense in the year we bought them.

  19. Hi, nice application. However I have 2 special delivery items to send that cost £35.65 each. I have stamps left from the days when I used to send a lot of post. Your site tells me I need 8 first class, check, 8 second class, oops, I only have 5. 8 first large, okay, and 7 second large, okay. But as I only have 5 second class stamps the calculator is useless for me. What would work better is where I can specify how many of each type of stamp I actually have.

    1. Hi,
      Not something I plan to add (I would have to rewrite it from scratch) but there’s a simpleish work around.
      a) work out the value of your 5xsecond class stamps (say 5x50p = £2.50″)
      b) deduct this from the total you seek (£35.00 – £2.50 = £32.50)
      c) Use the calculator to find the combinations to target £32.50 and set the second class value to 9999p. This stamp is then not included in the calculations (too expensive to be useful) and it will show you combinations of the remaining 3.

      Hope that helps

  20. Trevor john Wilkinson

    I have a large range of GB stamps with values from 1/2p to 68p. How can I decide which values to choose to get to £0.75. – £1.10. – £2.20. ? (I don’t mind if it takes up to 8 stamps).

    Thanks in advance.


  21. Trevor john Wilkinson

    How do you include 1/2p , 11.1/2p , 15.1/2p etc stamps in the calculator please?

    Thanks in advance.


    1. Sorry Trev, I only wrote this to handle a whole penny as the smallest unit!
      Do the post office still accept those?
      A work around is for the half penny stamps, keep them in pairs and each pair is 1p.
      for an 11.5p stamp, you can pair those to have 2 stamps as 23p.
      that’ll work until you’re almost out of those stamps, then you could pair an 11.5p + 0.5p stamp to make 12p for the last one
      hope that helps!

  22. trevor john wilkinson

    Thanks for your reply.
    Yes, the post office still accepts pictorials with the half penny stamps!

  23. Angela Cumming

    Royal Mail have increased their prices again from the 1st October 2023.
    Would you be able to update your stamputlor?
    I find this VERY useful. 🙂
    Many thanks

    1. Thanks for the prompt, stampulator now updated

  24. Nia Roberts

    Hi there – this is a terrifically useful tool; I use it all the time. I note that our beloved Royal Mail has upped the prices again though –

    1. Thanks for prompt, stampulator now updated

  25. This is really useful, as I’m now living far away from a post office! Thank you

  26. Hi Steve,
    I like your stampulator tool, it works great for me. I have two second class NVI (no value indicated) stamps. Can I use the two stamps on a 100g small letter to send the letter First Class? Or will it be treated as second class mail, because the stamps don’t show a value, they only show ‘2nd class’? Confused about this.

    1. They are valid at the current 2nd class rate. So using one 2nd class stamp will send the small letter 2nd class even if the prices have changed since you bought it.

      Make sure they’re the new style with the bar code on the stamp. If they are old I think you can still get them replaced free by Royal Mail.

  27. Joanne Greenwood

    Hi Steve, Thanks so much for this massively helpful tool. I did a big stamp swap, to surrender the old non-barcoded stamps, and got sheets and sheets of the new barcoded ones, whose value is just indicated as 1st or 2nd Large letter, etc. I intend to steadily use them for selling on ebay. So I will really need your calculator to help me with the maths!

    I have read your note that the Post office allow one to use a maximum of up to 9 of each type of stamp (thus 36 stamps in total). So as long as I do not break that rule, my question is: if I want to send a Small Parcel 1st Class (which as at today 27/03/24) would cost me £4.19 at the Post Office. But I want to send it 1st Class Signed for – which costs £5.39. Can I either put £5.39 on it in stamps (or the closest to it calculated with your calculator) and get proof of postage etc. as one option. Do I also have the another option of putting £4.19 on it (The current 1st Class Small Parcel fee) and paying the £1.20 difference in cash, which is the fee for the ‘Signed for’ part?

    Very many thanks, you are helping a lot of people with your website, Joanne

    1. Hi Joanne, thanks for commenting and I’m glad you’re finding it useful.

      The 9 stamp limit is actually a limit in the way I wrote the code. I decided you’d be unlikely to need more than 9 of each value of stamp but I also didn’t account for Royal Mail sending me only 1st class stamps as replacements to old stamps either 🙂
      In the calculator to use more than 9 x 1st class stamps, put: 125p in stamp 1, 125p in stamp 2, 9999p in stamp 3 and 9999p in stamp 4, then press submit.
      Result: for the 20Kg £11.99 parcel it says 1 x 1st (£1.25) + 9 x 125p, so 10 x first class stamps, and the result is 51p over the target value.

      Royal Mail let you have as many stamps as you need to reach the required postage value and as far I know there isn’t a limit on the number of stamps.
      You can pay more than the required value, but not less. You can set a custom target value if you need a service I haven’t listed, but ‘Signed for small parcel’ is in the table. Removing the 2nd and large options by putting a value of 9999 in the boxes at the top and pressing submit, the result is: £5.39 = 5 x 1st class stamps and is 86p more than you need to pay.

      You can also use the stamps you have to under the value (see ) and pay the difference at the post office when you hand over your letter and get your signed for receipt.
      That’s 4 x 1st class stamps and 39p to pay at the post office. Paying the extra is a better option if you have to wait for a receipt as then you can use up all your old stamps without paying more than you need to for the postage you need.

      Also worth saying, Royal Mail have had special pricing on parcels lately if purchased through their web site and that can come with free collection.

  28. Joanne Greenwood

    Brilliant Steve, thank you so much for your explanation and clarifying my misunderstanding on what I thought was a RM limit on number of stamps that can be used!
    I have had a play around with both calculators (so clever) and am rocking on full gas!
    I appreciate the values will change in the next few days, what with the price hike, and thanks again for your generous ‘public service’ . Best wishes, Joanne

  29. Roland Wastie

    Hi Steve
    only recently found your calculator ,brilliant.
    Only now Royal have done it again with price rises , I have stocked up with NV stamps just hope RM don’t go bust!!
    Thank you

    1. Thanks for the prompt, updated for 2024 prices now.

  30. Lynne Thompson

    I find this site very helpful, can this be change to reflect the new Royal Mail postage charges from April 2024

    1. Thanks for the prompt, updated to 2024 prices now

Leave a Reply

Your email address will not be published. Required fields are marked *

Search this site

Free apps

  • – Your birthday or other celebration date based on [years on other planets] / [how many seconds/days] / [how far you’ve travelled around the sun]
  • – Calculates the combination and how many 1st, 2nd, large 1st and large 2nd class Royal Mail stamps you need on large envelopes and packets

Recent posts