Aspect Ratio Calculator
Compute the missing width or height to maintain an aspect ratio.
Formula
Find missing W or H given ratio
How to use
- 1Enter the target ratio (for example 16 and 9).
- 2Enter the known width.
- 3Read the calculated height that keeps the ratio.
About this calculator
Resize an image by eye and it usually ends up stretched or squashed. The fix is to keep the aspect ratio, the fixed proportion between width and height, constant. Give this calculator a target ratio like 16:9 and one dimension, and it returns the other, so your image, video or layout scales cleanly with nothing distorted.
Formula explained
Height = Width × (Ratio Height ÷ Ratio Width). Rearranged, Width = Height × (Ratio Width ÷ Ratio Height). You are scaling one dimension by the ratio’s proportion so the shape does not change. The ratio is unitless.
Worked example
1920 × (9 ÷ 16) = 1080, so 1920 by 1080 (Full HD). Change the width to 1280 and the same ratio gives 720 (HD).
Tips & notes
- Match a platform’s native ratio on export to avoid cropping or letterboxing.
- The same ratio spans many resolutions, so note the pixel sizes you use most.
- When you must change ratio, crop deliberately rather than stretching.