Quick answer
UK paper sizes follow the international standard ISO 216. The most used sizes are A4 (210 × 297mm), A3 (297 × 420mm), A5 (148 × 210mm) and A6 (105 × 148mm). Every A size has the same proportions (a ratio of 1 to √2, about 1.414), so folding or cutting one in half gives the next size down: A3 halves to A4, A4 halves to A5. A0 has an area of one square metre. The B series sits between A sizes and is used for posters and books, while RA and SRA sizes are slightly larger press sheets that leave room for bleed and trimming.
Key takeaways
- A4 is 210 × 297mm (8.3 × 11.7 inches), or 2480 × 3508 pixels at 300dpi.
- Each A size is half the area of the one above it, with the same shape, so artwork scales between sizes without distortion.
- B sizes fall between A sizes. B2 (500 × 707mm) is the sheet size our Heidelberg litho presses are built around.
- SRA3 (320 × 450mm) is the standard digital press sheet. It holds two A4 pages with bleed, which is why A4 prints are trimmed from it.
- DL (99 × 210mm) is not an ISO A size. It is one third of A4, the finished size of an A4 sheet folded into three.
A paper sizes chart (A0 to A8)
The A series is the one most people mean by 'paper sizes'. It starts with A0, a sheet of one square metre, and each smaller size is made by halving the long side of the one before. The table gives each size in millimetres, inches and pixels at 300dpi, the resolution we recommend for print artwork.
| Size | Millimetres | Inches | Pixels at 300dpi | Typical uses |
|---|---|---|---|---|
| A0 | 841 × 1189 | 33.1 × 46.8 | 9933 × 14043 | Large posters, plans and display graphics |
| A1 | 594 × 841 | 23.4 × 33.1 | 7016 × 9933 | Posters, exhibition graphics |
| A2 | 420 × 594 | 16.5 × 23.4 | 4961 × 7016 | Posters, point-of-sale, wall planners |
| A3 | 297 × 420 | 11.7 × 16.5 | 3508 × 4961 | Small posters, menus, A4 brochures printed as a spread |
| A4 | 210 × 297 | 8.3 × 11.7 | 2480 × 3508 | Letters, letterheads, brochures, reports, flyers |
| A5 | 148 × 210 | 5.8 × 8.3 | 1748 × 2480 | Leaflets, flyers, booklets, notebooks |
| A6 | 105 × 148 | 4.1 × 5.8 | 1240 × 1748 | Postcards, small flyers, invitations |
| A7 | 74 × 105 | 2.9 × 4.1 | 874 × 1240 | Tickets, vouchers, small inserts |
| A8 | 52 × 74 | 2.0 × 2.9 | 614 × 874 | Labels, tags, small cards |
Pixels are for images, millimetres are for print
Pixel sizes tell you whether a photo or graphic has enough resolution to print sharply at that size. Set up the document itself in millimetres, with 3mm bleed on every trimmed edge. Our artwork set-up guide covers bleed, safe areas and PDF export.
Why A sizes fold so neatly: the √2 ratio
Every A size has a long side about 1.414 times its short side (the square root of 2). That ratio is the only one that keeps the same shape when a sheet is cut in half. In practice it means:
- A4 folded in half is A5, so an A4 sheet folds into an A5 leaflet and an A3 sheet folds into an A4 four-page brochure.
- Artwork scales between sizes without cropping or stretching. A design made for A4 enlarges to A3 or reduces to A5 at about 141% or 71%.
- Envelopes match. The C envelope series is sized to hold the matching A sheet, so C5 takes A5 flat or A4 folded once. See our envelope sizes guide.
Folds that are not in half, such as folding A4 into thirds, give sizes outside the A series. That is where DL comes from. Our guide to leaflet folds shows the finished size each fold gives.
B paper sizes
The B series fills the gaps between A sizes: each B size is the geometric mean of the A size above and below it. B sizes are used for posters, books and some envelopes, and, most importantly for printers, for press sheets.
| Size | Millimetres | Inches | Common uses |
|---|---|---|---|
| B0 | 1000 × 1414 | 39.4 × 55.7 | Very large posters |
| B1 | 707 × 1000 | 27.8 × 39.4 | Posters; the sheet size of larger litho presses |
| B2 | 500 × 707 | 19.7 × 27.8 | Posters; the sheet size of B2 litho presses such as ours |
| B3 | 353 × 500 | 13.9 × 19.7 | Posters |
| B4 | 250 × 353 | 9.8 × 13.9 | Books, large envelopes |
| B5 | 176 × 250 | 6.9 × 9.8 | Books, journals, notebooks |
| B6 | 125 × 176 | 4.9 × 6.9 | Paperbacks, small books |
Press sheet sizes: RA, SRA and what they mean for your job
Presses print on sheets larger than the finished piece. The extra paper allows for bleed, crop marks, colour bars and the grip edge the press holds the sheet by. The finished items are then trimmed out on a guillotine. The RA and SRA series, defined in ISO 217, are untrimmed sheets sized for this: RA sheets are 105% of the matching A area and SRA sheets are 115%.
| Sheet | Millimetres | What it is used for |
|---|---|---|
| SRA3 | 320 × 450 | Standard digital press sheet. Holds two A4 pages, or four A5, with bleed. |
| SRA2 | 450 × 640 | Larger digital and small-format litho sheets |
| SRA1 | 640 × 900 | Litho sheet for B1-class presses |
| RA3 | 305 × 430 | Untrimmed A3 with a small allowance for trimming |
| RA2 | 430 × 610 | Untrimmed A2 |
At Fretwell, our digital presses include two Ricoh Pro C651EX machines that take sheets up to 330 × 487mm, slightly larger than SRA3. Our litho floor runs two B2 Heidelberg presses: a Speedmaster XL 75 (maximum sheet 750 × 530mm) and a CX 74 (maximum sheet 720 × 520mm). A B2 sheet carries four A4 pages on each side, with room for bleed and trim, so an eight-page A4 brochure section prints on a single sheet.
This is why size affects price. A finished size that fits efficiently on the press sheet wastes less paper. A size just a few millimetres too big can drop the number of items per sheet and push the cost up. If you have flexibility on size, ask us before the design is fixed. Whether a job is best printed litho or digital depends on quantity as well as size.
B2 litho and digital print under one roof
Heidelberg Speedmaster litho and FOGRA-certified digital presses, with folding, binding and finishing in-house in Keighley.
Explore the serviceOther common print sizes
Some of the sizes printers use every day are not part of ISO 216. These are the ones we are asked about most:
| Size | Millimetres | Notes |
|---|---|---|
| DL | 99 × 210 | One third of A4. The finished size of an A4 sheet folded into three. Fits a DL envelope (110 × 220mm). |
| UK business card | 85 × 55 | The same size as a bank card. Set artwork up at 91 × 61mm to include 3mm bleed. |
| Square | Commonly 148 × 148 or 210 × 210 | Popular for invitations and brochures. Check postage format before choosing a square mail piece. |
| US Letter | 216 × 279 | The North American standard. Slightly wider and shorter than A4, so files set up for US Letter need resizing for UK print. |
For mailed items, the finished size decides the Royal Mail format and the envelope. Choose paper size, envelope and paper weight together, as all three affect the postage.
