How to use the aspect ratio calculator
- Choose Find a ratio to check an existing image or video, or Resize to a ratio to plan a new size.
- To find a ratio, type the width and height in pixels (or tap one of the common sizes). The simplified ratio, decimal, and nearest standard ratio update as you type.
- To resize, pick a preset like 16:9 or 4:5, or type any ratio into Custom ratio (16:9, 16x9, 2.35:1, and 2.35 all work). Then enter the side you already know, and the other side is calculated for you.
- Use a ratio often? Tap Save as preset to keep it in the preset row. You can also add your own sizes to the common sizes table.
- Leave Round to even numbers on for video exports. Turn it off for photos if you want the closest whole pixel.
- Use the copy buttons to paste the result straight into your editor, export settings, or code.
When it comes in handy
- Cutting one shoot for every platform. Work out the 9:16 frame for Reels, Shorts, and TikTok, the 4:5 frame for feed posts, and the 16:9 frame for YouTube from the same footage.
- Odd screen recordings. Find out what shape an unusual resolution really is, like 1366×768 or a cropped phone capture, and the nearest standard size to export to.
- Web and email images. Hit the exact height a theme, banner slot, or 1.91:1 link preview expects for a width you already know.
- Prints and covers. Check whether a photo's 3:2 shape will fit an 8×10 (5:4) or 4×5 frame, and how much will crop.
- Cinematic crops. Size letterboxed 2.39:1 or ultrawide 21:9 frames inside a 4K or HD timeline.
Frequently asked questions
What is an aspect ratio?
It's the shape of a frame, written as width to height. A 1920×1080 video and a 1280×720 video are different sizes but the same 16:9 shape. Ratios are reduced to the smallest whole numbers, so 1920:1080 becomes 16:9.
How do I calculate an aspect ratio by hand?
Divide the width and height by their greatest common divisor. For 1920×1080, the largest number that divides both is 120, giving 16 and 9. For the decimal form, divide width by height: 1920 ÷ 1080 = 1.778.
Why does my resolution give a strange ratio like 683:384?
Some resolutions don't reduce to a tidy ratio. 1366×768 is a common laptop screen that is almost, but not exactly, 16:9. The calculator shows the exact ratio and the nearest common one so you know what it's close to.
Why should video dimensions be even numbers?
Most video formats, including H.264 and H.265 in the usual 4:2:0 color format, store color at half resolution, so width and height need to divide evenly by 2. Odd sizes can cause export errors, a one-pixel black line, or a silent resize. Rounding to even avoids all of that.
What ratios do social platforms use?
As a rule of thumb, vertical short-form video (Reels, Shorts, TikTok, Stories) is 9:16, portrait feed posts are 4:5, square posts are 1:1, standard YouTube video is 16:9, and link preview images are about 1.91:1. Platforms change their specs from time to time, so check their help pages for exact current limits.
Is 21:9 the same as 2.39:1?
Close, but not identical. 21:9 works out to about 2.33, while the 2.39:1 cinema scope ratio is a little wider. Ultrawide monitors sold as 21:9 are often 2560×1080, which is closer to 2.37. Pick the preset that matches your actual delivery spec.
Does this tool upload anything?
No. Everything is calculated in your browser, and you only type in numbers. Nothing is sent to our server.