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UK paper weight and postage guide, 2026
Pick the right paper. Pay the right postage.
What gsm means, how thick each paper is, and what your mailing will cost at Royal Mail’s 2026 prices. Check a mailing in seconds before you print it.
- Royal Mail prices from 7 April 2026
- Weights worked out for you
- Free, with no sign-up
The two limits
Letter up to 100g
And up to 5mm thick
2nd Class 91p
Go over £1.55 or more
Stamp prices, 2026
Mailing checker
What will it weigh, and what will it cost to post?
A guide, not a quote. Prices are Royal Mail stamp prices for UK post from 7 April 2026. Weight is worked out from the paper; the envelope weight and the thickness are typical figures, so weigh and measure a finished sample before a big mailing. Check Royal Mail’s price finder.
Royal Mail prices, 2026
What it costs to post a letter in the UK
Stamp prices from 7 April 2026. A first class stamp rose 10p to £1.80 and a second class stamp rose 4p to 91p.
| Format | Weight | Largest size | 1st Class | 2nd Class |
|---|---|---|---|---|
| Letter | Up to 100g | 24 × 16.5cm, 5mm thick | £1.80 | 91p |
| Large Letter | Up to 100g | 35.3 × 25cm, 2.5cm thick | £3.30 | £1.55 |
| Large Letter | 101 to 250g | 35.3 × 25cm, 2.5cm thick | £3.60 | £1.90 |
| Large Letter | 251 to 500g | 35.3 × 25cm, 2.5cm thick | £3.60 | £2.40 |
| Large Letter | 501 to 750g | 35.3 × 25cm, 2.5cm thick | £3.60 | £2.70 |
100g
The weight limit
A Letter can weigh up to 100g, envelope included. That is about twelve sheets of 120gsm A4.
5mm
The thickness limit
A Letter can be no thicker than 5mm. Folding adds layers, so a thick mailing can fail on thickness before it fails on weight.
C5
The size limit
A4 sent flat in a C4 envelope is always a Large Letter. Fold it once into a C5 and it can go as a Letter: 91p, not £1.55.
Paper weights
What each paper weight is for
Gsm is the weight of one square metre of the paper. Higher numbers are heavier and usually thicker. The last column counts A4 sheets that stay inside 100g with a typical 7g envelope.
| Paper weight | Typical thickness | Good for | One A4 sheet | A4 sheets in a Letter |
|---|---|---|---|---|
| 80 to 100gsm | 100 to 125 microns | Everyday letters and internal documents | 5.0 to 6.2g | 14 to 18 |
| 120gsm | About 140 microns | Letterheads and compliment slips | 7.5g | 12 |
| 130 to 150gsm | 110 to 170 microns | Flyers and leaflets, brochure pages | 8.1 to 9.4g | 9 to 11 |
| 170gsm | 140 to 200 microns | Heavier flyers, posters, menus | 10.6g | 8 |
| 250gsm | 220 to 280 microns | Brochure covers, greeting cards | 15.6g | 5 |
| 300 to 350gsm | 280 to 420 microns | Postcards, invitations, folders | 18.7 to 21.8g | 4 |
| 400gsm and over | 400 microns and up | Business cards | 24.9g | 3 |
Thickness varies with the stock. Silk and gloss papers are pressed smooth, so they are thinner than an uncoated paper of the same weight. A micron is a thousandth of a millimetre.
Carrying and delivering it
How heavy is a box of 1,000 flyers?
Handy when you are booking a courier, loading a car for an event or handing boxes to a leaflet distributor. These are paper weights only, before packaging.
The sum: width in metres × height in metres × gsm = the weight of one sheet in grams.
So one A5 flyer on 300gsm is 0.148 × 0.210 × 300, which is 9.3g.
| 1,000 sheets | A6 | A5 | A4 |
|---|---|---|---|
| 130gsm | 2.0kg | 4.0kg | 8.1kg |
| 150gsm | 2.3kg | 4.7kg | 9.4kg |
| 170gsm | 2.6kg | 5.3kg | 10.6kg |
| 250gsm | 3.9kg | 7.8kg | 15.6kg |
| 300gsm | 4.7kg | 9.3kg | 18.7kg |
| 350gsm | 5.4kg | 10.9kg | 21.8kg |
Questions
Paper and postage, answered
What does gsm mean?
Grams per square metre: the weight of one square metre of the paper. Office paper is about 80gsm, a good flyer is 130 to 170gsm and a business card is 350gsm or more.
What is the difference between gsm and microns?
Gsm measures weight and microns measure thickness. They usually rise together, but not exactly: an uncoated paper is thicker than a silk or gloss paper of the same gsm.
How much is a stamp in 2026?
From 7 April 2026 a first class stamp is £1.80 and a second class stamp is 91p, for a Letter up to 100g. Large Letter stamps start at £3.30 first class and £1.55 second class.
How many sheets of A4 can I post with one stamp?
By weight, about 18 sheets of 80gsm or 12 sheets of 120gsm with a typical envelope. They must be folded into a C5 or DL envelope, and the finished letter must be no thicker than 5mm.
Is A4 always a Large Letter?
Only when it is sent flat. A C4 envelope is bigger than the Letter size limit of 24 × 16.5cm, so it is a Large Letter at any weight. Fold the A4 into a C5 or DL envelope and it can go as a Letter.
Can I post a postcard with a normal stamp?
Yes. An A6, A5 or DL card is inside the Letter size limit, so it needs one Letter stamp.
How do I work out the weight of a flyer?
Multiply the width in metres by the height in metres by the gsm. An A5 flyer on 300gsm is 0.148 × 0.210 × 300, which is 9.3g.
Are these prices for stamps or franking?
Stamps. Franking and business mail accounts are priced differently, usually a little lower. Royal Mail’s price finder has every service.
Can you help me choose a paper for a mailing?
Yes. Get in touch with what you are sending and how many, and a real person will suggest a paper that suits it.
Right paper.Right envelope.Right price.
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