Aspect Ratio Calculator
Enter any two of width, height and aspect ratio to get the third, such as 1920 × 1080 to 16:9.
Use Aspect Ratio Calculator
The 1 to 100,000 px range and the 1% rounding warning are Infinall guidelines, not platform rules. Free, no sign-up. Runs in your browser; nothing you enter is uploaded.
How to use it
Turn pixel sizes into an aspect ratio and back, so you can plan a crop or new size. If a side can't be a whole pixel, you see the exact value.
- Pick what to find: aspect ratio, height or width.
- Enter the other two values, such as a width and a ratio of 16 and 9.
- Read the result and how far rounding moves it off the ratio.
- Copy the size and resize your image with a tool below.
Formula
Ratio = width ÷ gcd : height ÷ gcd · Height = width × ratio height ÷ ratio width · Width = height × ratio width ÷ ratio height
Example
Kurta boutique, India: 4:5 crop
A Jaipur boutique crops a product photo of a ₹2,499 kurta for a portrait ad.
- Width
- 1,080
- Ratio width side
- 4
- Ratio height side
- 5
Questions
How do I work out the aspect ratio of an image from its pixels?
Divide the width and the height by the largest number that divides both. 1920 and 1080 share 120, so 1920 × 1080 becomes 16:9. The tool also gives the decimal form, 1.78:1: the long side divided by the short side.
Why does 1200 × 628 show 300:157 and not 1.91:1?
300:157 is the exact ratio (both sides divided by 4). 1.91:1 is the same shape rounded to two decimals, because 1200 ÷ 628 = 1.9108. Both forms appear, so you can use the format you need.
How do I find the height for a width at 16:9?
Multiply the width by 9, then divide by 16. A 1280 px width gives exactly 720 px. A 1080 px width gives 607.5, which is not a whole pixel, so the tool shows 608 px and says the size is 0.08% off the exact ratio.
What does "ratio off by" mean?
Images have whole pixels, so some sizes cannot hit a ratio exactly. The percentage compares the rounded size with the ratio you asked for. The tool adds a warning above 1%. For example, a 20 px wide 16:9 frame rounds to 11 px tall, which is 2.27% off.
Can I use a decimal ratio such as 1.91:1?
Yes. Enter 1.91 as the width side and 1 as the height side. Each side can have up to 4 decimals, and the tool uses the ratio exactly as typed rather than snapping it to a nearby fraction.
Does this calculator resize my image?
No. It only does the arithmetic. To make the file at that size, use one of the image resizers linked below.
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