---
title: "Aspect ratio calculator — free, runs in your browser"
description: "Scale a width or height while keeping the ratio, and identify the ratio of any size. Free, no sign-up, and nothing you enter leaves your browser."
url: https://atoneplace.net/tools/aspect-ratio-calculator/
site: "At One Place"
---

# Aspect ratio calculator

Scale a width or height while keeping the ratio, and identify the ratio of any size.

## How it works

Enter a width and height to get the simplified ratio, or lock a ratio and change one dimension to get the other. The ratio is simplified using the greatest common divisor, so 1920 × 1080 reports as 16:9 rather than 1920:1080.

Common ratios and where they come from: 16:9 is the broadcast and streaming standard; 4:3 was the old television and early computer shape; 3:2 is the classic 35 mm photograph and many laptop screens; 21:9 approximates the cinema widescreen ratio; 1:1 is the square used by several social platforms; 9:16 is vertical video.

Aspect ratio is independent of resolution. 1280 × 720 and 3840 × 2160 are both 16:9 — the ratio describes the shape, the resolution describes how many pixels fill it.

> This tool runs entirely in your browser. Nothing you enter is sent to a server, logged or stored, and the page keeps working with the network disconnected.

## Common questions

### What aspect ratio is 1920x1080?

16:9. Dividing both numbers by their greatest common divisor of 120 gives 16 and 9.

### How do you keep an image proportional when resizing?

Multiply both dimensions by the same factor. To fit a 1600 × 900 image into 1200 wide, scale by 1200 ÷ 1600 = 0.75, giving a height of 675.

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