Find a ratio, or the missing width or height. Runs on your device.
An aspect ratio compares width with height. The calculator divides the width by the height, then reduces both numbers to the smallest whole numbers that keep the same proportion. A 1920 by 1080 picture has the ratio 16:9: both sides are divisible by 120, and 1920 divided by 120 is 16, while 1080 divided by 120 is 9. The decimal form is the width divided by the height, so 16:9 is about 1.778 to 1. A ratio above 1 is landscape, below 1 is portrait, and exactly 1 is square. The closest common ratio is the one from a short list (1:1, 5:4, 4:3, 3:2, 16:10, 16:9, 2:1, 21:9, 4:5, 3:4, 2:3, 9:16 and 1:2) that is nearest to your numbers. The tool says whether the match is exact or only close. Use the ratio to describe a picture, a video frame or a layout, or to check that two sizes share a shape.
Pick a ratio, say which side you know, and type it. The other side is the known side multiplied by the ratio's other part and divided by the ratio's first part. For 16:9 at a width of 1280, the height is 1280 times 9 divided by 16, which is exactly 720. Not every answer is a whole number. At 16:9 and a width of 1000, the exact height is 562.5. The tool shows three outputs: the exact value to three decimals, the rounded whole number (halves go up, so 562.5 becomes 563), and the nearest even number (562 here). Even numbers matter because many video encoders need both sides to be even. When the exact value is not a whole number, the result says so and shows the rounding line. The common-widths table shows the height for five widths at the same ratio, so you can compare sizes at a glance.
Real sizes often sit near a common ratio without matching it. 1366 by 768 reduces to 683:384, which is close to 16:9 but not equal to it, so the tool shows 16:9 (close, not exact). 2560 by 1080 reduces to 64:27, and 3440 by 1440 reduces to 43:18. Both are near 21:9 and neither is equal to it, because 21:9 reduces to 7:3. The tool compares your numbers with the common list using exact arithmetic, so a match is only called exact when the two ratios are truly equal. The ratio you get is the one your numbers make, not a ratio the tool picks for you.
Each number can be above 0, with up to 6 digits before the point and up to 3 after it. Negative numbers, commas, exponents and fractions such as 16/9 are not accepted; write 1.778 instead. The numbers have no unit. Pixels, inches or millimetres all work, as long as both sides use the same unit, so 8.5 by 11 inches is 17:22. Mixing units, for example a width in pixels and a height in inches, gives a ratio that means nothing. The tool does not crop or resize an image, and it does not work out letterbox bars, DPI, print sizes or screen diagonals. Nothing you type is sent or stored. The page only keeps the mode, the ratio choice and which side you know.
16:9. Both sides divide by 120, leaving 16 and 9. As a decimal it is 1.778 to 1, and the shape is landscape.
720. Multiply 1280 by 9 and divide by 16. The answer is exact, so the tool shows no rounding line.
Some widths do not divide evenly into the ratio. At 16:9 and a width of 1000, the exact height is 562.5. The tool rounds halves up to 563 and shows 562 as the nearest even number, with the exact value beside them.
It is the closest even whole number to the exact value. Use it when a video encoder requires even width and height. At 16:9 and a width of 1000, the height 562.5 gives 562 as the nearest even number, while the rounded value is 563, which is odd.
No. It reduces to 64:27. The tool shows 21:9 as the closest common ratio with the note close, not exact, because 21:9 reduces to 7:3 and that is a different proportion.
Yes, when both sides use the same unit. An 8.5 by 11 inch sheet has the ratio 17:22, which is portrait. A width in millimetres with a height in inches gives a wrong ratio.