📐 Aspect Ratio Calculator

Enter a width and height to simplify the ratio using the greatest common divisor, and compare it to common named aspect ratios.

1. Simplify the ratio

Width (W)

Height (H)

Resize mode

Simplified ratio —

Closest named aspect ratio

—

16:9

2. Scale a dimension, preserving the ratio

Using the width/height ratio above, enter just a target width or height and the other dimension is computed automatically.

Target width

Target height

Box width

Box height

Common named aspect ratios

Ratio	Name	Typical use	Preset

💡 How to use the aspect ratio calculator

Use it when resizing video, banners, ads, thumbnails, or print layouts without distortion. Load common presets such as 16:9 YouTube thumbnails, 9:16 Shorts/Reels, 1:1 square feed posts, and 4:5 portrait feed posts, then check whether the asset should fit inside the box or fill it and crop.

GUIDE

Learn more

What is an aspect ratio?

An aspect ratio is the proportional relationship between width and height, usually written as W:H. A 1920×1080 resolution, for example, reduces to 16:9 when both numbers are divided by their greatest common divisor (120) — the most common ratio for Full HD and 4K video. Two images with the same ratio look the same shape (wide, square, tall) even if their actual pixel dimensions differ.

How the GCD simplifies a ratio

The Euclidean algorithm quickly finds the greatest common divisor (GCD) of two numbers, W and H. Dividing both by their GCD produces the simplest possible whole-number ratio. For instance, 1280×720 has a GCD of 80, simplifying to 16:9; 800×600 has a GCD of 200, simplifying to 4:3.

Resolution	GCD	Simplified ratio
1920 × 1080	120	16:9
1280 × 720	80	16:9
1080 × 1080	1080	1:1

Why doesn't it always match a standard ratio exactly?

Ratios with decimals, like the 2.35:1 cinemascope format, rarely divide evenly into real pixel resolutions. In that case the calculator flags the nearest standard ratio with a "closest match" badge, and shows "exact match" only when the computed ratio is within about 0.5% of a named ratio.

Fit vs fill and crop

Fit inside box keeps the whole image visible, so empty padding may remain when the source and box ratios differ. Fill and crop covers the whole box, but the overflow on one axis may be cropped. Check this before publishing thumbnails, ads, or social posts so text and faces stay inside the safe area.