PPI Calculator
Screen PPI, dot pitch and retina distance.
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Aspect Ratio Calculator
The missing dimension for any aspect ratio.
Aspect Ratio Calculator tool
Fill in one of these two.
Leave the one you want calculated empty.
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Missing dimension
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Aspect ratio
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As a decimal
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Common name
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New pixel count
| Format | Ratio | Height at this width |
|---|
Changing only one dimension and letting the other follow is what keeps an image from stretching. If the target size has a different ratio, something has to be cropped or letterboxed -- no resize can avoid it.
About the Aspect Ratio Calculator
Aspect Ratio Calculator finds the dimension you did not specify. Give it the original width and height and then either the new width or the new height, and it works out the other one so the proportions are preserved. That is the whole job of a resize: change one dimension and the other must follow, or the image stretches.
The simplified ratio comes from dividing both dimensions by their greatest common divisor, which is how 1920 x 1080 becomes 16:9. The calculator also names the ratio when it matches a standard format, because knowing a crop is 2.39:1 rather than 'roughly cinematic' is what lets you match it to a delivery specification.
When the target size has a different ratio from the original, no resize can satisfy both dimensions. Something has to give: crop the image, letterbox it, or accept distortion. The calculator says so rather than quietly stretching, and the format table shows what height each standard ratio would want at your chosen width, which is usually enough to pick the nearest sensible target.
The page shows its working, not just its answer. Where there is a formula it is printed with your own numbers substituted in, so you can check the result rather than take it on trust -- which is the difference between a calculator you can use for something that matters and one you cannot.
Everything runs inside your browser. What you type is never uploaded, never logged and never stored, and the calculator keeps working if your connection drops after the page has loaded.
Looking for something this does not cover? FreeToolStation.com is a second collection of the same kind of everyday tools, and it is worth a look if aspect ratio calculator is only part of what you are working on.
How to use the Aspect Ratio Calculator
- Enter original width, original height and new widthDecimals are fine, and thousands separators are accepted and ignored.
- Read the missing dimension, aspect ratio and as a decimalThe figures update as you type. The Calculate button is there if you would rather press something, but nothing waits for it.
- Copy or check the resultCopy the summary with the copy button, or open the table to check it row by row.
Features
- Shows missing dimension, aspect ratio, as a decimal, common name and new pixel count together, so you are not running it twice
- A results table you can read across
- Updates as you type, with no button to press and no page reload
- Copy the result in one click
- Free, no sign-up, and it runs entirely in your browser
Who uses this tool
The aspect ratio calculator is used by writers, developers, students, marketers and anyone else who needs the job done once without installing software. Common cases include:
- Resizing an image for the web without distorting it
- Finding the height for a 1280px-wide video
- Checking whether a crop matches 16:9 or 4:3
- Working out a thumbnail size from a source image
Frequently asked questions
Which box do I leave empty?
Whichever new dimension you want calculated. Fill in exactly one of the new width and new height.
What does 16:9 mean?
Sixteen units of width for every nine of height, a decimal ratio of about 1.778. It is the standard for HD video and most screens.
My result is not a whole number of pixels.
That is normal -- the exact figure is shown along with the rounded one. Rounding by one pixel is invisible; choose the rounded value.
How do I crop to a different ratio?
Pick the ratio you want from the table, note the height it needs at your width, and crop the difference off evenly from both sides.
Related tools
If the aspect ratio calculator is not quite what you need, these other free tools solve closely related problems, and there are 11 more in tech calculators.
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Ratio Calculator
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Checked and rebuilt on 2026-10-14. The method this calculator uses is described in the section above, and corrections go through the contact page.