Quick reference
What is aspect ratio?
The proportional relationship between width and height. 16:9 means for every 16 units wide, it's 9 units tall — regardless of actual pixel size.
Lock width vs height
Click the 🔓 icon beside a dimension to lock it. When locked, changing the ratio recalculates the other side — the locked value stays fixed.
Detect from image
Drop any image into the top area. The tool reads its pixel dimensions and calculates the exact ratio, auto-filling the calculator.
Why does the ratio simplify?
Custom ratios like 1920:1080 reduce to their simplest form (16:9) using GCD. This shows the true proportional relationship.