How do you find the ratio of a print size?
Divide both sides by the largest number that goes into both. 16x20 divides by 4 to give 4:5, and 24x36 divides by 12 to give 2:3. Two sizes share a ratio when the short side divided by the long side gives the same number: 8/10 and 16/20 are both 0.8.
Pixels are the size in inches times the dpi. For centimetres, divide by 2.54 first; for millimetres, by 25.4. The pixel numbers below are rounded to the nearest whole pixel, and they match the 300 dpi table on Pro Lab’s help page for the sizes it lists (Pro Lab: file resolution and quality). Sizes are listed short side first; for landscape, swap the numbers.
Which sizes are 2:3?
The 2:3 ratio (0.667) is the shape of a 35 mm film frame and of many camera sensors, so it fits photos with the least cropping.
| Size | Inches | Centimetres | Pixels at 300 dpi | Pixels at 150 dpi |
|---|---|---|---|---|
| 4x6 in | 4 x 6 | 10.2 x 15.2 | 1,200 x 1,800 | 600 x 900 |
| 20x30 cm | 7.9 x 11.8 | 20 x 30 | 2,362 x 3,543 | 1,181 x 1,772 |
| 8x12 in | 8 x 12 | 20.3 x 30.5 | 2,400 x 3,600 | 1,200 x 1,800 |
| 10x15 in | 10 x 15 | 25.4 x 38.1 | 3,000 x 4,500 | 1,500 x 2,250 |
| 12x18 in | 12 x 18 | 30.5 x 45.7 | 3,600 x 5,400 | 1,800 x 2,700 |
| 40x60 cm | 15.7 x 23.6 | 40 x 60 | 4,724 x 7,087 | 2,362 x 3,543 |
| 16x24 in | 16 x 24 | 40.6 x 61 | 4,800 x 7,200 | 2,400 x 3,600 |
| 20x30 in | 20 x 30 | 50.8 x 76.2 | 6,000 x 9,000 | 3,000 x 4,500 |
| 60x90 cm | 23.6 x 35.4 | 60 x 90 | 7,087 x 10,630 | 3,543 x 5,315 |
| 24x36 in | 24 x 36 | 61 x 91.4 | 7,200 x 10,800 | 3,600 x 5,400 |
Which sizes are 3:4?
The 3:4 ratio (0.75) includes 18x24 in, a common poster size, and the 30x40 and 60x80 cm frames.
| Size | Inches | Centimetres | Pixels at 300 dpi | Pixels at 150 dpi |
|---|---|---|---|---|
| 6x8 in | 6 x 8 | 15.2 x 20.3 | 1,800 x 2,400 | 900 x 1,200 |
| 9x12 in | 9 x 12 | 22.9 x 30.5 | 2,700 x 3,600 | 1,350 x 1,800 |
| 30x40 cm | 11.8 x 15.7 | 30 x 40 | 3,543 x 4,724 | 1,772 x 2,362 |
| 12x16 in | 12 x 16 | 30.5 x 40.6 | 3,600 x 4,800 | 1,800 x 2,400 |
| 45x60 cm | 17.7 x 23.6 | 45 x 60 | 5,315 x 7,087 | 2,657 x 3,543 |
| 18x24 in | 18 x 24 | 45.7 x 61 | 5,400 x 7,200 | 2,700 x 3,600 |
| 60x80 cm | 23.6 x 31.5 | 60 x 80 | 7,087 x 9,449 | 3,543 x 4,724 |
Which sizes are 4:5?
The 4:5 ratio (0.8) holds the classic 8x10 frame size.
| Size | Inches | Centimetres | Pixels at 300 dpi | Pixels at 150 dpi |
|---|---|---|---|---|
| 4x5 in | 4 x 5 | 10.2 x 12.7 | 1,200 x 1,500 | 600 x 750 |
| 20x25 cm | 7.9 x 9.8 | 20 x 25 | 2,362 x 2,953 | 1,181 x 1,476 |
| 8x10 in | 8 x 10 | 20.3 x 25.4 | 2,400 x 3,000 | 1,200 x 1,500 |
| 40x50 cm | 15.7 x 19.7 | 40 x 50 | 4,724 x 5,906 | 2,362 x 2,953 |
| 16x20 in | 16 x 20 | 40.6 x 50.8 | 4,800 x 6,000 | 2,400 x 3,000 |
| 24x30 in | 24 x 30 | 61 x 76.2 | 7,200 x 9,000 | 3,600 x 4,500 |
Which sizes are 5:7 and 11:14?
These two ratios are close (0.714 and 0.786) but neither matches 4:5, so 5x7 and 11x14 frames each need their own crop.
| Size | Ratio | Inches | Centimetres | Pixels at 300 dpi | Pixels at 150 dpi |
|---|---|---|---|---|---|
| 5x7 in | 5:7 | 5 x 7 | 12.7 x 17.8 | 1,500 x 2,100 | 750 x 1,050 |
| 10x14 in | 5:7 | 10 x 14 | 25.4 x 35.6 | 3,000 x 4,200 | 1,500 x 2,100 |
| 50x70 cm | 5:7 | 19.7 x 27.6 | 50 x 70 | 5,906 x 8,268 | 2,953 x 4,134 |
| 20x28 in | 5:7 | 20 x 28 | 50.8 x 71.1 | 6,000 x 8,400 | 3,000 x 4,200 |
| 11x14 in | 11:14 | 11 x 14 | 27.9 x 35.6 | 3,300 x 4,200 | 1,650 x 2,100 |
| 22x28 in | 11:14 | 22 x 28 | 55.9 x 71.1 | 6,600 x 8,400 | 3,300 x 4,200 |
Which sizes are ISO A?
The A sizes share the ratio 1:√2 (0.707): cut one in half across its long side and you get the next size down in the same shape. A0 is 841 x 1189 mm, and each smaller size is rounded down to the millimetre, so A5 (148 x 210 mm) is 0.3% off the exact ratio (ISO 216 on Wikipedia).
| Size | Millimetres | Inches | Pixels at 300 dpi | Pixels at 150 dpi |
|---|---|---|---|---|
| A5 | 148 x 210 | 5.8 x 8.3 | 1,748 x 2,480 | 874 x 1,240 |
| A4 | 210 x 297 | 8.3 x 11.7 | 2,480 x 3,508 | 1,240 x 1,754 |
| A3 | 297 x 420 | 11.7 x 16.5 | 3,508 x 4,961 | 1,754 x 2,480 |
| A2 | 420 x 594 | 16.5 x 23.4 | 4,961 x 7,016 | 2,480 x 3,508 |
| A1 | 594 x 841 | 23.4 x 33.1 | 7,016 x 9,933 | 3,508 x 4,967 |
| A0 | 841 x 1189 | 33.1 x 46.8 | 9,933 x 14,043 | 4,967 x 7,022 |
What happens if a file is printed at another ratio?
It gets cropped or gets a border. A 2:3 file printed on 8x10 paper is too long by a fifth: the print shop either cuts the ends off or shrinks it and leaves white bands at the sides. That is why the printable wall art size maker makes a separate crop for each ratio and lets you place it, instead of leaving the cut to the print shop.