Aspect Ratio Calculator
Simplify W×H to a ratio, or derive the missing dimension from a target ratio. 8 common presets.
published
- [FREE]
- [NO_SIGNUP]
- [NO_UPLOAD]
An aspect ratio calculator answers “what is the ratio of these dimensions?” and “if width/height is X, what’s the other dimension?” Three modes cover both directions.
Common presets
| Ratio | Where |
|---|---|
| 16:9 | HD/4K video, modern monitors |
| 4:3 | Classic TV, older monitors |
| 21:9 | Ultrawide monitors |
| 1:1 | Instagram square, profile pics |
| 9:16 | TikTok / Reels / Stories vertical |
| 3:2 | 35mm photography |
| 2.39:1 | Cinematic widescreen |
| 5:4 | Large format photo |
Privacy
Pure JS math. No upload, no analytics.
Related tools
- Image Size Converter — resize while preserving ratio.
- Image Format Converter — change format.
Frequently asked questions
What is aspect ratio?
Width divided by height, expressed as W:H. 1920×1080 is 16:9 because gcd(1920,1080)=120 and 1920/120=16, 1080/120=9. Used for video, photos, monitors, canvas sizing.
When do I derive height from width (or vice versa)?
When you know one dimension and a target ratio. Embedding a 1280-wide hero image at 16:9? Height = 1280 × 9 / 16 = 720. Setting a CSS aspect-ratio for responsive video? Same math.
Why is 2.39:1 in the presets?
Standard widescreen cinematic format (anamorphic Panavision). Approximated as 239:100. Other common cinematic ratios: 1.85:1 (Academy flat), 2:1 (Univisium).
Does this work with non-integer ratios?
Yes — input fractional ratios like 1.85 by 1, or 2.39 by 1. The derived dimension is computed as a float and rounded to 2 decimals on display.
Privacy?
Pure JS math in your browser. No upload.