Aspect ratio calculator. Lock the shape, solve the size.
Ratio locked. Edit width or height and the other follows. Click the lock to free both and read off the ratio instead.
Calculated locally. Nothing is sent anywhere.
Exact ratios, simplified automatically
Enter any width and height and the calculator reduces it to its simplest whole-number ratio using the greatest common divisor, so 1920×1080 reads as 16:9 and 2560×1600 reads as 16:10. Lock the ratio to resize without distortion, or unlock it to discover the ratio of a size you already have. Decimal ratios like 2.39:1 work too. It runs entirely in your browser, free forever.
How to use the Aspect Ratio Calculator
This calculator keeps a width and height in proportion. With the ratio locked it solves the missing side for you, and with it unlocked it measures any size and reduces it to the smallest whole-number ratio using the greatest common divisor. It is for designers, video editors and developers resizing images, video frames, screens and social posts.
Step by step
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Set the ratio
Type the shape into Ratio width and Ratio height, which start at 16 and 9, or click a chip under Common ratios such as 4:3, 1:1, 21:9, 9:16 or 2.39:1. Decimal ratios are fine.
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Solve the missing side
With the lock closed, type a number into Width or Height under Dimensions (pixels). The other side recalculates as you type. For example, at 16:9 a Width of 1280 gives a Height of 720.
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Measure a size you already have
Click the lock button between Width and Height to open it. Now both sides are independent: type any width and height and the Ratio width and Ratio height fields update to the simplified ratio. Click the lock again to scale proportionally from the current width.
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Use a preset size
Under Video & screen pick sizes such as 1080p, 4K UHD, DCI 4K or Cinema 2.39. Under Social & photo pick IG Portrait, IG Story / Reel, YT Thumb, LinkedIn, Pinterest or A4 photo. A size chip fills both dimensions and sets the ratio to match.
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Flip the orientation
Click Portrait or Landscape under the Preview to swap the ratio and the dimensions together, so 1920 by 1080 becomes 1080 by 1920 without any stretching.
Reading the result
- The green panel shows the current size in pixels. Its label reads Scaled to keep ratio when the lock is closed and Measured ratio when it is open.
- Simplified ratio is the size reduced by its greatest common divisor. The default 1920 by 1080 reads 16 : 9, and 2560 by 1440 also reads 16 : 9.
- Decimal (W÷H) is width divided by height, rounded to four places. For 1920 by 1080 it is 1.7778.
- Total pixels is width times height in megapixels. 1920 by 1080 is 2.0736 MP.
- The Preview rectangle draws the shape to scale, and the small badge above the dimension fields repeats the ratio.
Tips and common mistakes
- Decimal ratios are scaled to whole numbers before they are simplified, so 2.39 and 1 reads as 239 : 100. Both describe the same shape.
- Some real sizes do not reduce to a familiar ratio. 1366 by 768 is roughly 16:9 but simplifies to 683 : 384, so check the Decimal (W÷H) value when you only need to know if two sizes match.
- When the lock is closed, editing Ratio width or Ratio height keeps the current width and recalculates the height.
- Solved sides can come out as decimals, such as 1366 at 16:9 giving 768.375. Round to a whole pixel yourself before exporting.
Privacy and limits
All the math runs in your browser. Nothing you type is sent anywhere or saved, so a reload starts again at 16:9 and 1920 by 1080. Once the page has loaded it keeps working without a connection.
Every dimension question, answered.
Frequently asked questions.
Is the Aspect Ratio Calculator free?
Is it private? Is anything uploaded?
Does it work offline?
What does the lock button do?
How does the ratio simplification work?
Published · Last updated .
