Aspect Ratio Calculator
Calculate, simplify, and convert aspect ratios from width and height. Solve missing dimensions for any ratio.
Common aspect ratios
Two calculators in one: paste a width and height to get the simplified aspect ratio (e.g. 1920x1080 reduces to 16:9), or lock a ratio and enter one dimension to compute the other. Preset buttons for 16:9, 4:3, 21:9, 1:1, and 3:2 make sizing decisions faster. Everything runs in your browser with no upload or signup needed.
Aspect ratio describes the proportional relationship between width and height. It is written as two numbers separated by a colon, like 16:9, where both numbers have been divided by their greatest common divisor to reach the smallest whole-number form. A frame that is 1920x1080 pixels has the same shape as one that is 1280x720, 854x480, or any other resolution that reduces to 16:9.
The two most common tasks are simplification and dimension solving. Simplification takes a raw pixel size and tells you which named ratio it matches, which helps when a client sends dimensions without specifying the ratio or when you inherit an old asset. Dimension solving works the other way: you know the ratio and one side, and need the other side that will preserve the shape exactly. For example, a 16:9 canvas at 800 pixels wide needs a height of 450 pixels; rounding to the wrong integer would introduce black bars or cropping.
Common use cases span video production (where 16:9 dominates broadcast and streaming), photography (3:2 is the native ratio of most DSLRs), web design (container ratios for responsive embeds), and print layout. The 21:9 ultrawide ratio matters for cinematic video and monitor sizing. Knowing your target ratio before resizing or cropping prevents distortion and keeps pixel math consistent across a project.
- 1
Simplify a size
Enter a width and height in the Simplify tab. The calculator divides both values by their greatest common divisor and shows the reduced ratio instantly.
- 2
Pick a ratio and known dimension
Switch to the Solve tab, choose a preset or type a custom ratio, select whether you know the width or height, then enter the value.
- 3
Read the computed dimension
The missing dimension appears immediately along with the formula used, so you can verify the math before applying it to your project.
Video production
Confirm a timeline resolution is truly 16:9 before export, or find the correct height for a custom-width render without distorting the frame.
Responsive web embeds
Calculate padding-bottom percentages for CSS aspect-ratio boxes so video or map iframes scale correctly on all screen widths.
Photography and print
Determine crop dimensions when printing a 3:2 photo at a non-standard paper size to avoid unwanted white borders.
UI and game design
Keep sprite sheets, thumbnails, and UI panels proportional when resizing assets for multiple screen densities.
How does ratio simplification work?
The calculator finds the greatest common divisor (GCD) of the width and height using Euclid's algorithm, then divides both values by it. 1920 and 1080 share a GCD of 120, giving 16:9.
Why does the solved height sometimes differ by one pixel?
Integer pixel dimensions can't always represent an exact ratio, so the result is rounded to the nearest whole number. A one-pixel difference is normal and invisible in practice.
What is a decimal ratio and when do I use it?
The decimal ratio (width divided by height) is used in some software APIs, CSS aspect-ratio values, and camera specs. 16:9 equals approximately 1.7778. Both forms describe the same shape.
Is my data sent to a server?
No. All calculations run directly in your browser using JavaScript arithmetic. No numbers are transmitted anywhere, and there is no account or login.
Can I use non-standard ratios like 2.39:1?
Yes. In the Solve tab, type any numbers into the ratio fields. Cinemascope anamorphic formats like 2.39:1 (or equivalently 239:100) are fully supported alongside the standard presets.