Aspect Ratio Calculator
Resize width and height proportionally, find the aspect ratio of any dimensions and match common ratios like 16:9 and 4:3. Free and instant.
Dimensions
Ratio
Resize to a ratio without doing the division
Enter a width and a height in pixels and the calculator shows the simplified ratio (1920 × 1080 becomes 16:9), the decimal ratio to four places, the total pixel count in megapixels, and whether the shape is landscape, portrait or square, with a preview box drawn in proportion. A copy button puts the dimensions on the clipboard as "width x height".
With the ratio locked, editing one dimension recalculates the other, which is the usual job: you know the width a layout needs and want the matching height for a 16:9 video or a 3:2 photo. Unlock to type both values freely, then lock again to capture whatever shape is on screen as the new ratio. Preset buttons apply 16:9, 4:3, 1:1, 21:9, 3:2, 9:16, 2:3 and A4 paper to the current width.
Results are rounded to whole pixels, so the 16:9 height for a 1000-pixel width comes out as 563 rather than 562.5, and the simplified ratio is reduced from the rounded values with a greatest-common-divisor step. Odd dimensions therefore sometimes simplify to an unexpected pair (1000 × 563 is 1000:563, not 16:9); use the decimal ratio to confirm how close you are. Everything runs in the browser.
Frequently asked questions
How do I calculate an aspect ratio?
Divide both the width and the height by their greatest common divisor. 1920 and 1080 share a divisor of 120, giving 16:9; 1280 and 720 share 80 and give the same ratio.
What height is 16:9 for a given width?
Multiply the width by 9 and divide by 16. A 1280 width gives 720, a 1920 width gives 1080, and a 1000 width gives 562.5, which the calculator rounds to 563.
Does it resize the image file?
No. It works out the numbers only; apply them in whatever editor you are using. It does not read or modify image files.
What aspect ratio is A4 paper?
210 × 297 mm, which simplifies to 70:99 and is 1:1.414 as a decimal, the square root of two. The A4 preset applies that shape to the current width.
Why does my ratio not simplify to 16:9?
Because the dimensions are not exact multiples of 16 and 9. Rounding to whole pixels can leave a height one pixel off, and the simplified ratio reports the exact pair you entered. Check the decimal ratio: 1.7778 is 16:9 regardless of how the integers reduce.