Aspect Ratio Calculator
Enter a width or height with a target aspect ratio and instantly get the matching dimension plus the simplified ratio.
Aspect Ratio Calculator — An aspect ratio calculator for resizing images, videos and layouts without distortion. Pick a preset ratio like 16:9, 4:3, 1:1 or 21:9 (or type your own), enter the width or the height, and the other dimension is filled in automatically while the ratio is kept. The simplified width:height fraction is shown too. Every calculation runs entirely in your browser, so the numbers you type never leave your device.
What is Aspect Ratio Calculator?
The Aspect Ratio Calculator is a free in-browser tool for keeping the correct proportions when you scale something. Designers, video editors, photographers and developers use it to find a missing width or height for a given ratio, to check what ratio a set of dimensions actually has, or to reduce a pair of numbers to its simplest form. Choose a preset with the segmented buttons (16:9, 4:3, 1:1, 21:9) or switch to 'Custom' and type your own ratio in the settings. Then type into the width field or the height field; whichever you edit last becomes the anchor, and the calculator computes the other side to keep the ratio. The read-only result fields and the reduced-fraction stat update as you type, and empty or invalid entries simply show a dash.
How to use Aspect Ratio Calculator
- Choose a preset aspect ratio with the segmented buttons: 16:9, 4:3, 1:1 or 21:9.
- For a different ratio, pick 'Custom' and open the settings to type your own width:height ratio.
- Type a number into the width field, or into the height field — whichever value you know.
- Read the other dimension in the read-only result fields; it recalculates automatically to keep the ratio.
- Check the simplified width : height fraction shown under the results.
Examples
Height from width at 16:9
Input
Ratio 16:9, width = 1920
Output
Height = 1080 (ratio 16 : 9)
Width from height at 4:3
Input
Ratio 4:3, height = 600
Output
Width = 800 (ratio 4 : 3)
Custom ratio 2.39:1
Input
Custom ratio 2.39:1, width = 2390
Output
Height = 1000 (ratio 239 : 100)
Frequently asked questions
- How do I calculate the missing dimension?
- Pick a ratio (a preset or your own custom ratio), then type either the width or the height. The calculator keeps the ratio and fills in the other side. The field you edit last is treated as the source value.
- Can I use a custom ratio?
- Yes. Select 'Custom' on the preset bar and open the settings panel to enter your own width:height ratio. Decimal ratios such as 2.39:1 are supported.
- What is the simplified ratio shown below the results?
- It is the width-to-height ratio reduced to its smallest whole numbers using the greatest common divisor — for example 1920 : 1080 becomes 16 : 9. Decimal dimensions are scaled before reducing.
- What happens with empty or zero values?
- If the source field is empty or not a valid positive number, the results and the simplified ratio show a dash. A ratio side of zero is also treated as invalid because dividing by zero is undefined.
- Are my numbers sent to a server?
- No. The calculator is 100% client-side and runs entirely in your browser with no upload and no server communication, so the values you enter never leave your device.
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