The complete UK guide

Print, Paper & Frame Sizes

Every paper size from A0 to A8, the standard photo and art-print sizes, and exactly which frame and mount each one needs — in millimetres, centimetres and inches.

Updated June 202612 min read

Halve A0 and you get A1; halve again for A2, and so on — every size keeps the same 1 : √2 proportions.

We cut mounts and join frames by hand every day, and the question we answer most often isn’t about mouldings or glass — it’s about size. What’s A3 in centimetres? What frame fits an A4 print? Do I need a mount, and how wide should it be? This guide puts the whole chain in one place: paper → print → mount → frame, so you can go from a dimension to the right frame without guessing.

01ISO 216 standard

ISO A paper sizes, A0 to A8

The A series is the international standard for paper across the UK and Europe. It is built on one elegant rule: every size is exactly half the area of the one above, and they all share the same 1 : √2 proportion, so a design scales between them without ever changing shape.

Size	Millimetresw × h	Centimetres	Inches	Typical use
A0	841 × 1189	84.1 × 118.9	33.1 × 46.8	Large display & exhibition posters
A1	594 × 841	59.4 × 84.1	23.4 × 33.1	Posters, technical drawings
A2	420 × 594	42.0 × 59.4	16.5 × 23.4	Art prints, medium posters
A3	297 × 420	29.7 × 42.0	11.7 × 16.5	Prints, charts, double-page spreads
A4	210 × 297	21.0 × 29.7	8.3 × 11.7	The everyday sheet — letters, prints
A5	148 × 210	14.8 × 21.0	5.8 × 8.3	Notepads, flyers, small prints
A6	105 × 148	10.5 × 14.8	4.1 × 5.8	Postcards, greeting cards
A7	74 × 105	7.4 × 10.5	2.9 × 4.1	Compliment slips, tickets
A8	52 × 74	5.2 × 7.4	2.0 × 2.9	Labels, playing-card scale

All A-series dimensions are width × height in portrait orientation. Tolerances under ISO 216 are ±1–2 mm.

This is why an A4 design enlarges cleanly to A3 for a poster, or shrinks to A5 for a flyer — the proportions never distort. It also makes framing predictable: a mount cut for an A4 print drops straight into a standard A3 frame, which is the single most common combination we cut.

ISO B sizes — notebooks, books & posters

The B series runs alongside the A series for things that don’t suit an A size — most notebooks, many books, and posters. Each B size is the geometric mean of two A sizes, so it slots neatly between them: B5, the classic notebook, is larger than A5 but smaller than A4.

Size	Millimetresw × h	Centimetres	Inches	Typical use
B0	1000 × 1414	100 × 141.4	39.4 × 55.7	Large posters & display
B1	707 × 1000	70.7 × 100	27.8 × 39.4	Posters
B2	500 × 707	50 × 70.7	19.7 × 27.8	Posters, large prints
B3	353 × 500	35.3 × 50	13.9 × 19.7	Posters, large sketchbooks
B4	250 × 353	25 × 35.3	9.8 × 13.9	Sketchbooks, art books
B5	176 × 250	17.6 × 25	6.9 × 9.8	The classic notebook & book size
B6	125 × 176	12.5 × 17.6	4.9 × 6.9	Pocket notebooks
B7	88 × 125	8.8 × 12.5	3.5 × 4.9	Passport-scale notebooks
B8	62 × 88	6.2 × 8.8	2.4 × 3.5	Mini notes & labels

B5 and B6 are the everyday notebook sizes; B6 fits a coat pocket. Larger B sizes (B0–B2) are common for posters where A sizes feel a touch small.

North American paper sizes

Framing a print from the US? North America doesn’t use the A series — it uses the Letter and ANSI standards instead. The sizes are close to their A-series cousins but never identical, so it’s worth checking before you buy a frame.

Size	Millimetresw × h	Centimetres	Inches	Typical use
US Letter	216 × 279	21.6 × 27.9	8.5 × 11	The everyday US sheet — wider & shorter than A4 (ANSI A)
US Legal	216 × 356	21.6 × 35.6	8.5 × 14	Contracts & legal documents
Tabloid / Ledger	279 × 432	27.9 × 43.2	11 × 17	US posters & spreads (ANSI B)
ANSI C	432 × 559	43.2 × 55.9	17 × 22	Engineering & display prints
ANSI D	559 × 864	55.9 × 86.4	22 × 34	Large technical drawings
ANSI E	864 × 1118	86.4 × 111.8	34 × 44	Large-format posters & plans

US Letter (8.5 × 11″) is 6 mm wider and 18 mm shorter than A4 (210 × 297 mm) — visibly different in a frame, so the two aren’t interchangeable.

02Photographic prints

Standard photo print sizes

Photo sizes are quoted in inches in the UK and don’t follow the A series. The size you choose depends on your camera’s aspect ratio — print to the wrong ratio and the lab will crop your image to fit.

Size	Centimetres	Millimetres	Ratio	Best for
6 × 4″	15.2 × 10.2	152 × 102	3:2	The standard print — straight off a DSLR or 35mm
7 × 5″	17.8 × 12.7	178 × 127	7:5	Desk frames & small gifts
8 × 6″	20.3 × 15.2	203 × 152	4:3	Phone photos (4:3 sensor) without cropping
10 × 8″	25.4 × 20.3	254 × 203	5:4	Portraits — the classic mantelpiece size
12 × 8″	30.5 × 20.3	305 × 203	3:2	Landscapes & panoramic-leaning shots
12 × 10″	30.5 × 25.4	305 × 254	6:5	A generous frame size for a single portrait
14 × 11″	35.6 × 27.9	356 × 279	14:11	Statement prints, group shots
20 × 16″	50.8 × 40.6	508 × 406	5:4	Wall-scale enlargements

6 × 4″ (3:2) matches DSLR and 35 mm film. Phone photos are usually 4:3 — print them at 8 × 6″ to avoid cropping.

Square formats

Square prints came into their own with Instagram and record-sleeve-style display. They sit outside the standard series, so they almost always want a custom mount.

Size	Centimetres	Best for
5 × 5″	12.7 × 12.7	Instagram-format minis
8 × 8″	20.3 × 20.3	Album & record-sleeve scale
12 × 12″	30.5 × 30.5	Statement square prints

03Art prints & posters

Art print & poster sizes

Modern art prints are sold in metric sizes drawn from the European gallery standard, while posters and older prints often come in imperial. Knowing both saves you buying a frame that’s a centimetre out.

Metric — the gallery standard

Size	mm	Inches
30 × 40 cm	300 × 400	11.8 × 15.7
50 × 70 cm	500 × 700	19.7 × 27.6
60 × 80 cm	600 × 800	23.6 × 31.5
70 × 100 cm	700 × 1000	27.6 × 39.4

Imperial — posters & US prints

Size	Centimetres
11 × 14″	27.9 × 35.6
16 × 20″	40.6 × 50.8
18 × 24″	45.7 × 61.0
24 × 36″	61.0 × 91.4

If you buy art prints online, 30 × 40 cm and 50 × 70 cm are the two sizes you’ll meet most — they’re the backbone of the gallery-wall look. Both are non-standard against the A series, which is exactly why they so often arrive needing a made-to-measure mount.

Watercolour & fine-art paper sizes

Watercolour, drawing and printmaking papers follow the old imperial sheet sizes. They’re sold as a full sheet and torn or cut down by the artist, which means a finished watercolour rarely matches any frame standard — a custom mount is almost always the answer.

Sheet	Millimetresw × h	Inches	Typical use
Eighth Imperial	190 × 280	7.5 × 11	Small studies, greetings cards
Quarter Imperial	280 × 380	11 × 15	The everyday watercolour sheet
Half Imperial	380 × 560	15 × 22	Larger finished paintings
Full Imperial	560 × 760	22 × 30	The standard full sheet, as sold
Double Elephant	680 × 1010	27 × 40	Large exhibition watercolours

Sizes are approximate — handmade and mould-made papers carry deckled (torn) edges, so we measure the actual sheet and cut the mount to suit.

04The bit nobody explains

What size frame do you need for your print?

This is where most guides stop and most people get stuck. The frame you buy depends on one decision: are you mounting the print, or not? Here’s how the numbers actually work.

Without a mount, the frame is simply the same size as your print. An A4 print goes in an A4 frame; a 50 × 70 cm print goes in a 50 × 70 cm frame. Clean and contemporary, and the image fills the whole opening.

With a mount — the option we recommend for anything on paper — the frame steps up a size to make room for the border. The mount’s aperture (the window the image shows through) is cut a few millimetres smaller than the print on every side, so the edges sit tucked behind the board rather than floating.

Mounted size = the frame you buy. Aperture = the window, cut ~5 mm smaller than the print all round.

Common print-to-frame combinations

Your print	Mount aperturemm	Mount border	Frame to buy
A5 (148 × 210)	138 × 200	40 mm	A4 (210 × 297)
6 × 4″ photo	142 × 92	~55 mm	8 × 8″ / 20 × 20 cm
A4 (210 × 297)	200 × 287	45 mm	A3 (297 × 420)
10 × 8″ photo	244 × 193	50 mm	14 × 11″ / 36 × 28 cm
30 × 40 cm	290 × 390	50 mm	40 × 50 cm
A3 (297 × 420)	287 × 410	55 mm	A2 (420 × 594)
50 × 70 cm	490 × 690	60 mm	70 × 90 cm
A2 (420 × 594)	410 × 584	65 mm	A1 (594 × 841)

Apertures shown are a guide — we cut each one to your exact print so nothing slips. Borders are the visible mount width on each side.

05Mounts & mat boards

Choosing the right mount

A mount is the quiet decision that makes a frame look considered. It sets the artwork back from the glass and gives the eye a margin of calm — but border width, layers and board quality all matter.

How wide should the border be?

As a rule, the border should grow with the print. Too narrow and it looks like a mistake; generously wide reads as deliberate and gallery-grade.

Print size	Border	Why
Small — up to A4 / 10×8″	40 – 50 mm	Enough air to lift the image without overwhelming it
Medium — A3 to A2 / 16×20″	50 – 70 mm	Scales the breathing room with the print
Large — A1 and above	70 – 100 mm	A wide border reads as deliberate, gallery-grade

Single vs double

A single mount is one board. A double mount adds a second, slightly smaller board beneath it, leaving a thin reveal of colour around the aperture — a subtle line that lifts the work.

Bottom-weighting

Cut the bottom border a few millimetres wider than the others. The picture then sits optically centred rather than mathematically centred — a framer’s trick the eye reads as right.

Conservation grade

Ordinary mount card is acidic and, over years, leaves a brown “mat burn” line on the artwork. Conservation and cotton-museum boards are acid-free and pH-buffered — essential for anything you want to keep.

06The cheat sheet

Quick-reference lookup chart

The fast answer. Find your print on the left, then read across to the frame you need — flush, or with a mount.

Your print	Frame — no mount	Frame — with mount
6 × 4″ photo	6 × 4″ frame	8 × 6″ frame + 6×4 mount
7 × 5″ photo	7 × 5″ frame	10 × 8″ frame + 7×5 mount
10 × 8″ photo	10 × 8″ frame	14 × 11″ frame + 10×8 mount
A5 print	A5 frame	A4 frame + A5 mount
A4 print	A4 frame	A3 frame + A4 mount
A3 print	A3 frame	A2 frame + A3 mount
A2 print	A2 frame	A1 frame + A2 mount
30 × 40 cm	30 × 40 frame	40 × 50 cm frame + aperture
50 × 70 cm	50 × 70 frame	70 × 90 cm frame + aperture

Non-standard sizes (square prints, 30 × 40, 50 × 70 cm) almost always want a made-to-measure mount cut to the exact image.

Made to measure

Order a custom window mount

Tell us the print size and we cut the aperture to the exact millimetre — single or double, in conservation board. Ready in days.

Configure your mount Readymade & bespoke

Browse our frame collections

From standard A-size frames to bespoke mouldings hand-joined in SE1. Bring a print in, or build it online.

See the framing range

Common questions

Frequently asked questions

What size frame do I need for an A4 print?

If you frame the print edge-to-edge with no mount, you need an A4 frame (210 × 297 mm). If you want a mount border around it — which we recommend for prints and artwork — the usual choice is an A3 frame (297 × 420 mm) with an A4 aperture cut into the mount. That gives roughly a 45 mm border on every side.

What is the difference between A4 and A3?

A3 is exactly twice the area of A4. Place two A4 sheets side by side along their long edge and you get an A3 sheet. A4 is 210 × 297 mm; A3 is 297 × 420 mm. The whole A series works this way — each size up doubles the one below it.

What is a mount (or mat)?

A mount is the card border between your artwork and the frame. It does two jobs: it sets the picture back from the glass so the surface can breathe and never sticks to it, and it gives the eye a margin of calm space that makes the work read as framed rather than pinned. A window mount has an aperture cut through it that the image shows through.

How wide should a mount border be?

For most prints up to A4 or 10 × 8″, a 40 – 50 mm border looks balanced. Scale it up with the print: 50 – 70 mm for A3 to A2, and 70 mm or more for A1 and larger. A common traditional touch is to make the bottom border a few millimetres wider than the others so the picture sits optically centred rather than mathematically centred.

What is a 6 × 4 photo in centimetres?

A 6 × 4 inch photo is 15.2 × 10.2 cm, usually rounded to 15 × 10 cm. It is the standard photographic print size and has a 3:2 aspect ratio, which matches most DSLR and 35 mm camera sensors.

Can I frame a print without a mount?

Yes. Framing without a mount — sometimes called a flush or print-to-edge frame — gives a cleaner, more contemporary look and lets the image fill the whole opening. You simply choose a frame the same size as the print. We do recommend a mount for anything on paper you want to keep long-term, as it stops the artwork touching the glass.

What is the most popular art-print size in the UK?

For modern gallery-wall prints, 30 × 40 cm and 50 × 70 cm are the two most-sold sizes, both drawn from the European metric standard. For traditional and photographic work, A3, A4 and 10 × 8″ remain the staples.

Is A4 the same as US Letter size?

No. A4 is 210 × 297 mm (8.3 × 11.7″); US Letter is 216 × 279 mm (8.5 × 11″). A4 is narrower and taller. If you are framing an American print or document, check which standard it was printed to before buying a frame.

What does "mounted size" mean when buying a frame?

Mounted size is the outer dimension of the artwork once the mount is added — in other words, the size of the frame you need. The "aperture" or "window" is the smaller opening the image shows through, cut a few millimetres smaller than the print so its edges sit behind the board.