Aspect Ratio Calculator
Find the simplified aspect ratio, decimal ratio, and pixel diagonal for any resolution or dimension pair.
Results
What is it?
The aspect ratio is the proportional relationship between a display width and height expressed as W:H. A 1920x1080 display has the same 16:9 ratio as a 3840x2160 (4K) display — they just have different pixel densities.
How to use
Enter the width and height of your resolution or physical dimensions. The calculator uses the Euclidean algorithm to find the greatest common divisor (GCD) and reduces the ratio to its simplest form. It also shows the exact decimal ratio and pixel diagonal.
Example scenario
A 2560x1080 ultrawide monitor: the simplified ratio is 64:27 (a true 21:9 is approximately 21.333:9, so this is close). The decimal ratio is 2.3704 — noticeably wider than 16:9 (1.7778). Pixel diagonal = 2,775 px.
Pro tip
When scaling video, multiply both ratio parts by the same integer to get equivalent resolutions. Letterboxing (black bars on top/bottom) occurs when video is wider than the screen ratio; pillarboxing (bars on sides) occurs when video is narrower. Common ratios: 4:3 (old TV/monitor), 16:9 (HD/4K standard), 21:9 (ultrawide cinema).