Aspect Ratio Calculator

Aspect Ratio Calculator reduces a width and a height to the smallest whole ratio and a decimal. 1920 by 1080 is 16:9 and 1.7778.

Divide by the greatest common divisor

The fields open on 1920 and 1080. The button says Calculate. Width and height are rounded to integers before the divisor is taken. That divisor is divided out of both numbers. The ratio line is those two results joined by a colon. The decimal line is the raw width divided by the raw height, printed with up to four fraction digits. 1920 and 1080 share a divisor of 120, so the ratio is 16:9. 1920 divided by 1080 is 1.7778 on that line. The labels are Ratio and Decimal. A width or height that is not positive stops with Width and height must be positive.

What the decimal is for

16:9 is the same shape as 1920:1080, written smaller. The decimal is useful when a form wants one number, such as 1.7778, instead of a pair. It is not a pixel size. This page does not crop a picture and it does not resize one. A photo crop that keeps a ratio is a different tool. DPI tools answer pixels per inch. Do not type a ratio you already know, such as 16 and 9, and expect a screen size back. You would get 16:9 again and a decimal of 1.7778, which only confirms the pair.

Rounding before the colon

Because the ratio uses rounded integers, 1920.4 by 1080.4 is treated as 1920 by 1080. A size that is almost a standard ratio can still print an awkward pair if the integers do not share a large divisor. 1366 by 768 is not forced to 16:9. Read the ratio the tool prints. The decimal still uses the numbers you typed, before that integer rounding, so the two lines can disagree slightly on a fractional input. 1366 divided by 768 is about 1.7786 on the decimal line, while the colon pair is whatever the integers reduce to.

When you need a picture instead

This form has no file picker. If the job is to cut a photo, leave this page. If the job is to know what 800 by 600 reduces to, type those pixels. 800 and 600 reduce with a divisor of 200, which is 4:3, and the decimal is 1.3333. 1280 by 720 shares a divisor of 80 and prints 16:9, with a decimal of 1.7778, the same decimal as 1920 by 1080. 100 by 100 is 1:1 and the decimal is 1. 2560 by 1440 is also 16:9. A 4 by 3 pair is already reduced, so the ratio line repeats 4:3. The numbers stay in this browser. Last checked: October 2026, against aspectRatio.