Aspect Ratio Calculator
Work out the missing width or height for any aspect ratio — or find the ratio of a size you already have. Pick a preset or type your own.
Enter the size you have — the ratio is reduced to its simplest form.
Calculators for popular ratios
Each one starts with the ratio set and lists the standard sizes for it.
What is an aspect ratio?
An aspect ratio describes the shape of a rectangle: its width compared to its height, written as two numbers separated by a colon. A 16:9 image is 16 units wide for every 9 units tall, whatever its actual size — 1280 × 720, 1920 × 1080 and 3840 × 2160 all share the same 16:9 shape.
How to calculate the missing side
Divide the side you know by its part of the ratio, then multiply by the other part.
width = height × W ÷ H
For a 1920-pixel-wide image at 16:9: 1920 × 9 ÷ 16 = 1080 px. For a 1440-pixel-tall image at 16:9: 1440 × 16 ÷ 9 = 2560 px.
How to find the aspect ratio of a size
Divide both sides by their greatest common divisor. 1920 and 1080 share a divisor of 120, so 1920 × 1080 reduces to 16:9. Some sizes do not reduce to a familiar ratio — 2560 × 1080 is exactly 64:27 — so the calculator also shows the closest standard ratio (here 21:9) and the decimal value (2.370).
Common aspect ratios
- 16:9 — widescreen video, TVs, monitors, YouTube.
- 9:16 — vertical video for TikTok, Reels, Shorts and Stories.
- 4:3 — classic TV, many compact cameras, iPad screens.
- 3:2 — most DSLR and mirrorless camera sensors, 6 × 4 in prints.
- 1:1 — square posts, profile pictures, album covers.
- 4:5 — portrait posts in the Instagram feed.
- 21:9 — ultrawide monitors and cinematic video.
Why whole pixels matter
Screens and image files work in whole pixels, so a calculated side such as 1080 × 607.5 has to be rounded. With “Whole pixels” ticked the calculator rounds to the nearest pixel and shows the exact value underneath, so you can see how far the rounded size is from the true ratio.
Frequently asked questions
How do I find the aspect ratio of an image?
Switch to “Find a ratio” and enter the width and height in pixels. The calculator reduces them to the simplest ratio and shows the closest standard one.
Is 1920 × 1080 the same as 16:9?
Yes. 1920 ÷ 1080 = 1.777…, which is exactly 16 ÷ 9.
How do I resize an image without changing its aspect ratio?
Choose the new width (or height), keep the same ratio and let the calculator work out the other side. Then scale the image to exactly that size.
What is the difference between aspect ratio and resolution?
Resolution is the number of pixels (for example 1920 × 1080). Aspect ratio is the shape those pixels form (16:9). Many resolutions share one aspect ratio.