Photo print sizes from A4 to 70 × 100 cm

The A series under ISO 216

A sizes are defined by the international standard ISO 216. A0 has an area of one square metre and sides in the ratio 1 : √2 (about 1 : 1.414). Halving the longer side produces the next size down with the same ratio. That is why A3 can be reduced to A4 without cropping.

Size	Dimensions in mm	Dimensions in cm
A0	841 × 1189	84.1 × 118.9
A1	594 × 841	59.4 × 84.1
A2	420 × 594	42.0 × 59.4
A3	297 × 420	29.7 × 42.0
A4	210 × 297	21.0 × 29.7
A5	148 × 210	14.8 × 21.0
A6	105 × 148	10.5 × 14.8

Sizes such as A3+ or A2+ are not part of the standard. Paper manufacturers use them for sheets that are slightly larger, so that an A3 or A2 image fits with a border.

Photo print sizes

Photo print sizes are given in centimetres and do not share a single aspect ratio. The actual paper size can vary by a few millimetres from lab to lab; 10 × 15 cm, for instance, derives from the 4 × 6 inch size (10.16 × 15.24 cm).

Size	Aspect ratio	From a 3 : 2 photo	From a 4 : 3 photo
10 × 15 cm	3 : 2	no crop	short side cropped by 11%
13 × 18 cm	1.38 : 1	92% of the long side remains	96% of the short side remains
20 × 30 cm	3 : 2	no crop	short side cropped by 11%
30 × 40 cm	4 : 3	89% of the long side remains	no crop
40 × 60 cm	3 : 2	no crop	short side cropped by 11%
50 × 70 cm	7 : 5	93% of the long side remains	95% of the short side remains
60 × 90 cm	3 : 2	no crop	short side cropped by 11%
70 × 100 cm	10 : 7	95% of the long side remains	93% of the short side remains

3 : 2 sizes are the most convenient for camera photographs. Phone pictures (mostly 4 : 3) fit 30 × 40 cm. The 50 × 70 and 70 × 100 cm sizes have a ratio close to the A series, so frames and mounts in these sizes are common too.

How to decide on a size

1. Pixels first. Find out how large a print the file can take at your chosen PPI. There is a table in DPI, PPI and resolution.
2. Then the space. Judge the size against the room. The Size on the wall tool shows A4 to 70 × 100 cm above a desk, sofa, bed or chest of drawers.
3. Then the frame. A frame and mount add several centimetres on every side. A 30 × 40 cm photograph in a mounted frame can measure 50 × 60 cm or more on the outside. See Mounts.
4. Crop it yourself. If you send a file in a different aspect ratio from the print size, the lab will crop it automatically, usually from the centre. Cropping it yourself makes sure the head or the horizon stays where it should.

Square and panoramic

Square sizes (20 × 20, 30 × 30, 50 × 50 cm) suit images from 6 × 6 cm medium-format cameras and crops from phone pictures. Panoramas are usually printed at ratios from 2 : 1 to 3 : 1. With these, check the pixel count of the short side especially carefully: a 12,000 × 4000 px panorama is only 33.9 cm high at 300 PPI.