Aspect Ratio Calculator
Reduce a width and height to its simplest ratio, match an image to the frames passport and photo specs use (1:1, 7:9, 5:7 …), or find the missing side for a target width or height. Nothing is uploaded — the numbers stay in your browser.
Enter a width and height (in any unit), or the pixel dimensions of an image.
Match a preset ratio
Pick a preset ratio, then enter a target width or height.
How the numbers relate
- Ratio = width ÷ height, reduced by their greatest common divisor. 35 × 45 reduces to 7:9; 50 × 70 reduces to 5:7; a square is 1:1.
- Same ratio, any size. 7:9 fits 35 × 45 mm, 413 × 531 px or 700 × 900 px — the shape is identical, only the scale changes.
- Find the missing side. height = width × (ratio h ÷ ratio w); width = height × (ratio w ÷ ratio h).
- Never fix a ratio by stretching. Forcing the wrong-shaped image into a frame squashes the face; crop to the ratio first, then size to pixels.
Ratios passport and photo specs use
National standards reduce to a handful of shapes. A US visa and the DV lottery are 1:1 (51 × 51 mm, 600 × 600 px at 300 dpi); most European passports and visas are 7:9 (35 × 45 mm, 413 × 531 px); the Chinese ID frames are 5:7 (25 × 35 mm and 35 × 49 mm); China's passport page is 11:16 (33 × 48 mm, 354 × 472 px). Crop to the shape first and the pixel dimensions second — see every format on the photo size chart, and check a finished file with the passport photo checker.
Related tools
Crop to the ratio with the image cropper; work out pixels-per-inch with the DPI calculator; scale the pixels with the image resizer; and lay out prints with the photo print sheet.
Frequently asked questions
What is the aspect ratio of a 600 × 600 photo?
1:1 — a square. 600 and 600 reduce to 1:1, which is the US visa, US passport and DV lottery shape.
What ratio is a 35 × 45 mm passport photo?
7:9. 35 and 45 share a factor of 5, so 35:45 reduces to 7:9 — the frame used by most European passports and visas.
How do I reduce a ratio to its simplest form?
Divide both numbers by their greatest common divisor. 50 and 70 divide by 10, giving 5:7.
How do I find the height for a given width?
Multiply the width by the ratio's height and divide by its width. For 7:9 at 600 px wide, the height is 600 × 9 ÷ 7 ≈ 771 px.
Does cropping to the right ratio also fix the pixel size?
No — the ratio fixes the shape, not the resolution. Crop to the ratio, then export at the pixel size the specification asks for.
Is a 4:5 ratio the same as 8 × 10 inches?
Yes. 8 and 10 reduce by 2 to 4:5, so an 8 × 10 print is a 4:5 frame.
Honest limits: this is arithmetic on the numbers you type, not a scan of your file — it does not read an image’s pixel dimensions. The preset pixel figures are the ones published on this site’s photo size chart and maker specifications; confirm the exact rule on the destination’s official page before you submit.
Related: photo size chart · image cropper · DPI calculator · passport photo checker · all tools