Enter the original dimensions and either a new width or new height to scale while keeping the ratio.
An aspect ratio describes the proportional relationship between a rectangle's width and height. Common ratios include 16:9 (widescreen video), 4:3 (traditional TV and monitors), 1:1 (square), and 3:2 (35mm film). The simplified ratio is found by dividing both dimensions by their greatest common divisor (GCD).
To scale an image or video, keep the ratio constant: new height = original height x (new width / original width).
To calculate an aspect ratio, divide the width and height by their greatest common divisor (GCD) to get the simplest whole-number ratio; to scale a new width or height, multiply by the ratio between the new and original dimension. Example: 1920x1080 simplifies to 16:9, and scaling to a 1280-pixel width gives a height of 1280 x 1080 / 1920 = 720.
1920x1080 is 16:9 (gcd is 120; 1920÷120=16, 1080÷120=9), the standard Full HD ratio.
1280x720 is 16:9 (gcd is 80; 1280÷80=16, 720÷80=9), the standard HD ratio.
3840x2160 (4K UHD) is 16:9 (gcd is 240; 3840÷240=16, 2160÷240=9), the same ratio as 1080p at four times the pixel count.
1080x1350 is 4:5 (gcd is 270; 1080÷270=4, 1350÷270=5), the Instagram portrait post ratio.
At 16:9, a width of 1600 pairs with a height of 900 (1600 × 9 ÷ 16 = 900).
1920x1200 is 8:5 (gcd is 240; 1920÷240=8, 1200÷240=5), also known as WUXGA or 16:10.
| Width x Height | Simplified ratio | Common name |
|---|---|---|
| 1920 x 1080 | 16:9 | Full HD widescreen |
| 1280 x 720 | 16:9 | HD widescreen |
| 3840 x 2160 | 16:9 | 4K UHD |
| 1024 x 768 | 4:3 | Traditional monitor |
| 2560 x 1440 | 16:9 | QHD widescreen |
16:9 is the standard for widescreen video, television, and most modern monitors and phone screens in landscape mode, adopted as part of the HDTV standard. Resolutions like 1280x720, 1920x1080, and 3840x2160 (4K) all share this same 16:9 ratio.
This tool uses the Euclidean algorithm: repeatedly divide the larger number by the smaller and replace the larger with the remainder, until the remainder is 0. The last non-zero remainder is the GCD, which is then used to reduce the ratio to its simplest form.
Pixel dimensions must be whole numbers because a screen or video frame cannot have a fractional pixel. When scaling produces a decimal result, this tool rounds to the nearest whole pixel, which can introduce a tiny rounding difference in the exact ratio.
4:3 is the traditional, more square-shaped ratio used by older televisions and monitors, like 1024x768. 16:9 is wider and is now the standard for widescreen video, HDTV, and most modern displays.
This calculator finds the simplified whole-number ratio and scales one dimension from the other; it rounds results to the nearest whole pixel and does not account for pixel aspect ratio differences used in some broadcast video formats.
Sources: ITU-R Recommendation BT.709 - HDTV parameter values (16:9 standard)
Last updated: 2026-08-17