Aspect ratio calculator
Reduce an integer ratio exactly, or calculate a missing width or height from a ratio and one known dimension.
How to use
Enter ratio width and height and choose reduction or the missing dimension. Supply known height when calculating width, or known width when calculating height. Generate, check whether the displayed result is exact or rounded, then copy or download the text.
1920:1080 reduces to 16:9. With that ratio, height 720 gives width 1280, and width 320 gives height 180.
Support & limits
Reduction uses the greatest common divisor and BigInt without integer precision loss. Dimensions use exact rational decimal arithmetic, then round to 6 decimal places with ties away from zero; trailing zeroes are removed. A positive result below half of 10⁻⁶ can display as 0, with a rounding notice. No whole-pixel rounding or unit detection is applied; keep units consistent. Download contains only the ratio or calculated dimension, followed by LF.
Common questions
Does this resize an image?
No. This is a numerical calculator and reads no files. Use the image resize tool to change image pixels.