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.

15 thoughts on “How many 1st class stamps to use on heavy letters?”

  1. 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.

  2. 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 🙂

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

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

      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.

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

  6. 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!

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