1920x1080 reduces to 16:9
Dividing both numbers by their greatest common divisor, 120, gives 16 and 9 — the standard widescreen ratio.
Aspect ratio calculator
Enter any pixel width and height and this tool reduces them to their lowest-terms aspect ratio using the same greatest-common-divisor math behind every ratio you've seen — 1920x1080 reduces to 16:9, for example, because their greatest common divisor is 120. Presets fill in common social media export sizes so you can check them in one click.
Common presets
16:9
Simplified by dividing both dimensions by their greatest common divisor, 120.
- Decimal ratio
- 1.7778
- Closest common ratio
- 16:9 (exact)
Formula
ratio = width ÷ gcd(width, height) : height ÷ gcd(width, height)
How to use the aspect ratio calculator
- Enter your width and height in pixels. Type the exact pixel dimensions of your image or video export.
- Or click a common preset. Presets like Full HD, square and vertical Reel sizes fill both fields for you in one click.
- Read the simplified ratio. The result shows your dimensions reduced to their lowest terms, plus the divisor used to get there.
- Compare against the closest common ratio. The result also names the nearest standard ratio, like 16:9 or 4:5, and whether your input matches it exactly.
- Re-export if your ratio does not match your target platform. A mismatched ratio often means a platform will crop your media rather than resize it evenly.
Worked examples
1080x1350 reduces to 4:5
Dividing both numbers by their greatest common divisor, 270, gives 4 and 5 — a common Instagram portrait ratio.
Aspect ratio calculator FAQ
- How is the aspect ratio calculated?
- Both the width and height are divided by their greatest common divisor, found using the Euclidean algorithm, to reach the smallest whole-number ratio.
- Why does 1920x1080 become 16:9 instead of some other ratio?
- Because 120 is the largest number that divides evenly into both 1920 and 1080, and dividing both by it gives exactly 16 and 9.
- What if my dimensions do not match a common ratio exactly?
- The calculator still simplifies them precisely and separately names the closest common ratio, so you can see how far off you are.
- Does this tool resize or crop my actual image?
- No — it only calculates the ratio from the numbers you type in; no file is uploaded or modified.
- What aspect ratio should I use for a Reel or Short?
- A vertical 9:16 ratio, commonly 1080 by 1920 pixels, is the standard export size for Reels, TikTok and Shorts.
- Does the calculator store or send my dimensions anywhere?
- No — the calculation happens entirely in your browser as you type, and nothing is uploaded or saved.
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