Aspect Ratio Calculator
Solve for a missing width or height from any aspect ratio, or reduce two dimensions to their simplest ratio.
About the Aspect Ratio Calculator
The Aspect Ratio Calculator takes the guesswork out of resizing images, videos, and layouts. Give it an aspect ratio — pick a common preset like 16:9 or type your own W:H — then enter just one dimension, and it instantly returns the matching width or height. Working the other way around? Switch to "Find ratio," enter your original width and height, and it reduces them to the simplest whole-number ratio and shows the decimal equivalent too.
Getting proportions right matters more than it seems. Stretch a 16:9 video into a 4:3 frame and faces distort; crop a square thumbnail from a widescreen still and you lose the edges. Whether you're prepping a YouTube thumbnail, sizing a social banner, exporting for a specific screen, or just matching two elements in a design, keeping the aspect ratio locked means your content scales cleanly without squishing or letterboxing. This tool does the small but fiddly arithmetic for you so every export lands at the right shape on the first try.
Everything runs directly in your browser. Nothing you type is uploaded, saved, or shared — the math happens locally on your device, so it's fast, private, and keeps working even offline once the page has loaded.
How to use
- Choose a mode. Use "Solve dimension" when you know the ratio and one side. Use "Find ratio" when you have a width and height and want the ratio itself.
- Set the aspect ratio (Solve mode). Tap a preset such as 16:9, 4:3, 1:1, 9:16, or 21:9, or type any custom values into the ratio width and height fields.
- Enter one dimension. Type a known width to get the matching height, or a known height to get the matching width. You can fill both to see each result.
- Read the result. The panel shows the computed pixel dimension the moment you change an input.
- Or find a ratio. Switch to "Find ratio," enter your original width and height, and read the simplified ratio and its decimal value.
If a field is empty or set to zero, the tool simply shows a dash instead of a confusing error, so you'll never see "NaN."
Common ratios
- 16:9 — the standard widescreen ratio for YouTube, most displays, and TV.
- 4:3 — the classic ratio used by older screens, tablets, and many photos.
- 1:1 — a perfect square, popular for profile pictures and feed posts.
- 9:16 — vertical full-screen video for Stories, Reels, and TikTok.
- 21:9 — ultrawide cinematic format for films and wide monitors.
Frequently asked questions
How does the calculator find the missing dimension?
It scales your known side by the ratio. To get height from width it computes width × (ratio height ÷ ratio width); to get width from height it computes height × (ratio width ÷ ratio height). For example, a width of 1920 at 16:9 gives a height of 1920 × (9 ÷ 16) = 1080.
How is the simplified ratio calculated?
In "Find ratio" mode the tool divides both your width and height by their greatest common divisor (GCD). So 1920 × 1080 reduces to 16:9, and 1000 × 1000 reduces to 1:1. If either value isn't a whole number, it shows a decimal ratio in the form N:1 instead.
Can I use custom, non-preset ratios?
Yes. The presets are just shortcuts. In "Solve dimension" mode you can type any ratio width and height you like — for instance 3:2 for photography or 2.39:1 for anamorphic film — and the calculator works exactly the same way.
What is the decimal ratio for?
The decimal value is simply width divided by height. It's handy when a design tool or spec sheet asks for a single number (like 1.78 for 16:9) rather than a colon-separated pair. It gives you a quick way to compare two shapes at a glance.
Does it work with any unit, not just pixels?
Yes. The math is purely proportional, so the fields are labeled in pixels for convenience but the result carries whatever unit you put in. Enter inches, centimeters, or arbitrary units and the ratio scaling still holds — only the number matters, not the unit.
Is my data sent anywhere?
No. The Aspect Ratio Calculator runs entirely in your browser. Nothing you enter is transmitted, stored, or logged — all calculations happen locally on your device, which also means the tool keeps working offline once the page has loaded.