Aspect Ratio Calculator
Turn any pixel resolution into its simplest width-to-height ratio — and see the decimal value alongside.
Any resolution
Enter a width and height in pixels and the calculator reduces them to the smallest whole-number ratio, such as 16:9 or 4:3.
Whole pixels only
Aspect ratios are defined for positive whole-pixel dimensions — decimals or zero values have no meaningful ratio.
What is an aspect ratio?
Width to height, as the smallest whole numbers
An aspect ratio describes the proportion between an image or screen's width and its height. It strips a resolution down to its essence: 1920 × 1080 and 1280 × 720 look different on paper, but both are 16:9 — sixteen units of width for every nine of height. Because the ratio ignores the absolute pixel count, it is the standard way to describe screens, photos, and videos regardless of how large they are.
Enter the width and height in pixels to get the simplest whole-number ratio and the decimal ratio.
The ratio is just width : height, divided down by the largest number that goes into both — their greatest common divisor (GCD).
Aspect ratio = width : height, reduced by the GCDThe greatest common divisor is found with the Euclidean algorithm, the same method used to reduce a fraction to its lowest terms. Dividing both sides by it leaves the smallest pair of whole numbers that keeps the proportion exact. The decimal ratio — width ÷ height — is reported alongside for quick numeric comparison.
Suppose you have a Full HD screen at 1920 × 1080 pixels.
Find the GCD
The greatest common divisor of 1920 and 1080 is 120.
Divide both sides
1920 ÷ 120 = 16 and 1080 ÷ 120 = 9.
Read the ratio
The reduced ratio is 16:9, or about 1.7778 as a decimal.
The ratio tells you the shape of the frame at a glance. 16:9 (≈ 1.78) is today's standard for HD and 4K video, laptops, and phones held sideways. 4:3 (≈ 1.33) is the older, squarer format of classic monitors and many tablets. 21:9 (≈ 2.33) is the ultrawide and cinematic look, much wider than it is tall. 1:1 is a perfect square, common for social-media posts and avatars. A larger decimal means a wider frame; a value near 1 means an almost square one.
The reduction is exact, but a couple of points are worth keeping in mind.
Whole pixels, and cropping changes the ratio
The calculator expects positive whole-pixel dimensions — screens and image files are always measured in whole pixels, so decimal or zero inputs have no defined ratio. Note too that cropping an image changes its aspect ratio, because you remove pixels from one dimension; only scaling both sides by the same factor preserves it.