Aspect Ratio Calculator
Turn any width × height into its simplified aspect ratio (16:9, 21:9, 4:3…) and its decimal ratio — instantly, with zero pixels of ambiguity.
Aspect ratio answers the question "is this 16:9 or 21:9 or something weird?" Divide both dimensions by their greatest common divisor and the ratio falls out. It also tells you whether an image or video will letterbox on your monitor.
How it works
Find the greatest common divisor (gcd) of width and height, then divide both by it:
3440 × 1440 → gcd 80 → 43:18
43:18 is the exact ultrawide ratio; marketing rounds it to 21:9.
Example
1280×720 and 1920×1080 both reduce to 16:9 — same aspect, different scale.
The math behind it
gcd(w, h) → w/g : h/g · decimal = w ÷ h
Frequently Asked Questions
What does "21:9" actually mean on monitors?
The monitor reports 21:9, but true ultrawides are usually 64:27 = 2.333 — so-called 21:9. The calculator's exact simplified ratio shows the truth.
How do I know if a video fits my screen?
Match the video's simplified ratio to your monitor's. Differing ratios cause letterbox bars; some players stretch instead.