Aspect Ratio Calculator
Reduce two dimensions to their simplest ratio, find the missing width or height, and check a size against a ratio.
Browser onlyYour data never leaves this device.
Every calculation runs in your browser. Nothing you type is uploaded, stored, or logged, and the tool never opens or reads an image file.
Details: Privacy policy
Inputs
Enter a width, a height, or both.
Enter both dimensions to reduce them, one dimension plus a ratio to find the other, or both dimensions plus a ratio to check whether the size fits it. Widths and heights are whole pixels from 1 to 100,000.
Ratio terms accept up to 4 decimal places (for example 1.85:1); they are converted to exact integers before reducing, so nothing is inferred from a rounded float.
Result
No inputs yet.
Enter two dimensions, or one dimension plus a ratio.
Aspect Ratio Calculator works on numbers, not pictures: enter two dimensions and it reduces them to the simplest whole-number ratio, enter one dimension plus a ratio and it computes the missing side, or enter a size plus a target ratio and it reports whether they match. Reduction uses the Euclidean GCD, decimal ratio terms are converted to exact integers first, and every rounded result is shown together with the exact value it came from. Because ratios are unitless, pixels, centimetres and inches behave identically; the calculator never assumes a unit or silently converts one.
Key facts
- Input
- Two dimensions, or a ratio and one side
- Output
- Simplest ratio and any missing side
- Limits
- Dimensions are whole pixels from 1 to 100,000; the tool assumes no unit, physical size, or device. Ratio terms accept up to four decimal places and are converted to exact integers before reducing, so 1.85:1 is exact rather than a rounded float.
- Processing
- In your browser — nothing is uploaded
- Sign-up
- Not required
- Cost
- Free
Limits above are read from the same code that enforces them; formats are the ones the tool accepts and produces.
How to use Aspect Ratio Calculator
- Enter both dimensions to reduce them, one dimension plus a ratio to find the other, or all three to check the fit.
- Read the reduced ratio, the decimal value, and — when a side was computed — the exact and rounded values side by side.
- Copy the result, or use a common-ratio shortcut to fill the ratio field.
What you get
- The two dimensions reduced to their simplest ratio, with the exact decimal beside it.
- A missing width or height computed from the other dimension and a ratio, rounded half-up with the exact unrounded figure alongside.
- A match verdict decided by integer cross-multiplication, so being one pixel off is reported as a mismatch rather than rounded away.
When to use Aspect Ratio Calculator
- Work out the height for a 1000 px wide banner at 16:9 without guessing a round number.
- Check whether a screenshot, video frame, or export really matches 16:10 before shipping it.
- Reduce awkward dimensions such as 1920 × 1200 or 1366 × 768 to the ratio people recognise.
Frequently asked questions about Aspect Ratio Calculator
How do I find the height for a 16:9 image that is 1000 pixels wide?
Enter 1000 as the width and 16:9 as the ratio. The calculator computes 1000 × 9 ÷ 16 = 562.5 and reports 563 px rounded half-up, with the exact 562.5 px still visible so you can round differently on purpose.
Why does it say my size does not match the ratio?
The check uses exact integer cross-multiplication: for 16:9 it compares width × 9 with height × 16. Sizes that are within a pixel but not exactly proportional are reported as a mismatch, which is what you want when a platform letterboxes anything that is not exact.
Does this calculator resize or crop my image?
No. It only works with the numbers you type and never opens an image file. When you have the target dimensions, use Image Resizer for one image or Social Image Resizer for a set of preset sizes.
Can I use decimal ratios such as 1.85:1?
Yes, up to four decimal places. Decimal terms are converted to exact integers (1.85 becomes 18500/10000) before reducing, so the result comes from integer arithmetic rather than from a rounded floating-point value.
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