Aspect Ratio Calculator — How to Calculate and Scale Ratios
Find the simplified aspect ratio from width × height, then scale to a target width (or height). Presets 16:9, 4:3, and 1:1 stay options on one page. Example: 1920×1080 → 16:9; scale width to 1280 → height 720. Runs in your browser; numbers stay on your device and are not uploaded to a server.
How it works
Enter width and height (or pick a 16:9, 4:3, or 1:1 preset that fills common pixel sizes). The tool simplifies the pair with a greatest common divisor, then scales the other side when you set a target width or height. All math runs in your browser tab; your numbers are not uploaded to a server.
Formula and assumptions
Ratio simplification and proportional scaling use integer gcd on the input pair:
- Let g = gcd(round(W), round(H)). Simplified ratio = (W÷g):(H÷g).
- Scale by width: H′ = targetW × H ÷ W. Scale by height: W′ = targetH × W ÷ H.
- Presets only fill sample sizes (16:9 → 1920×1080, 4:3 → 1600×1200, 1:1 → 1080×1080); they are not separate pages.
Example
Example: width 1920 and height 1080. gcd(1920,1080)=120, so the ratio is 16:9. Scale width to 1280 → height = 1280 × 1080 ÷ 1920 = 720.
When to use it
- Pick an export size that keeps a 16:9 video frame without stretching.
- Match a design canvas to a phone or monitor ratio before exporting assets.
- Convert a known resolution into a short ratio label for specs or CSS planning.
Frequently asked questions
How is the aspect ratio simplified?
The calculator divides width and height by their greatest common divisor after rounding to whole numbers, so 1920×1080 becomes 16:9.
Why are 16:9, 4:3, and 1:1 only presets?
Those ratios are common starting points. Keeping them as options on one page avoids separate near-duplicate calculators for each preset.
Can I scale by height instead of width?
Yes. Switch “Scale by” to target height; the tool solves for the matching width while keeping the same ratio.
Are my numbers uploaded?
No. Dimensions are calculated in your browser on your device and are not uploaded to a server.
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