Aspect Ratio Calculator
Simplify any width × height to a ratio like 16:9, find the nearest standard ratio, resize to a new width or height, and list common resolutions.
Ratios are reduced with the greatest common divisor; decimals are scaled to whole numbers first.
| Size | Width × height | Exact? |
|---|---|---|
| 360p | 640 × 360 | exact |
| SD 480p | 853 × 480 | rounded from 853.33 |
| 540p | 960 × 540 | exact |
| HD 720p | 1280 × 720 | exact |
| 768p | 1365 × 768 | rounded from 1365.33 |
| 900p | 1600 × 900 | exact |
| Full HD 1080p | 1920 × 1080 | exact |
| 1200p | 2133 × 1200 | rounded from 2133.33 |
| QHD 1440p | 2560 × 1440 | exact |
| 1600p | 2844 × 1600 | rounded from 2844.44 |
| 4K UHD 2160p | 3840 × 2160 | exact |
| 2880p | 5120 × 2880 | exact |
| 8K 4320p | 7680 × 4320 | exact |
An aspect ratio is the proportion of width to height — 16:9 for HD video, 4:3 for older screens and iPads, 4:5 for Instagram portrait posts. This calculator reduces any size to its simplest ratio, tells you which standard ratio it is (or is closest to), and resizes it without distortion so you can scale images, video exports or embed boxes correctly.
How to use this tool
- Enter the original width and height in pixels (any unit works as long as both match).
- Optionally enter a new width or new height to get the other side, or both to fit the image inside a box.
- Or enter a scale percentage; tick "round to even" for video sizes.
- For anamorphic video, enter the pixel aspect ratio to get the display aspect ratio.
Formula
ratio = (W ÷ g) : (H ÷ g), where g = gcd(W, H). New height = new width × H ÷ W; new width = new height × W ÷ H. Display aspect ratio = W × PAR ÷ H.
gcd is the greatest common divisor. The nearest standard ratio is chosen by the smallest difference on a logarithmic scale, so 1.79:1 and 1.77:1 are treated symmetrically around 16:9.
Example
For 1920 × 1080, gcd(1920, 1080) = 120, so the ratio is 1920/120 : 1080/120 = 16:9 (1.7778:1). Resizing to a width of 1280 gives 1280 × 1080 ÷ 1920 = 720, so 1280 × 720. A 1366 × 768 laptop screen reduces only to 683:384 — about 0.05% wider than 16:9.
Frequently asked questions
Is 21:9 really 21:9?
Not exactly. "21:9" ultrawide monitors are 2560×1080 (64:27 ≈ 2.37:1) or 3440×1440 (43:18 ≈ 2.39:1). The name is marketing shorthand for roughly 2.33–2.4:1.
Why round to even numbers?
Most video codecs store color at half resolution (4:2:0 chroma subsampling), so width and height must be divisible by 2. Encoders reject or pad odd sizes.
What is the difference between 16:9 and 16:10?
16:10 (1.6:1) is slightly taller than 16:9 (1.78:1). 1920×1200 is 16:10; 1920×1080 is 16:9. Laptops often use 16:10 for extra vertical space.
Last updated:
Page address with these inputs: https://kakao.mobile/tools/aspect-ratio-calculator/
Cite or embed this tool
kakaoCalc. (2026, November 8). Aspect Ratio Calculator. https://kakao.mobile/tools/aspect-ratio-calculator/
“Aspect Ratio Calculator.” kakaoCalc, 8 Nov. 2026, kakao.mobile/tools/aspect-ratio-calculator/.
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