Image Aspect Ratio Calculator
Work out a proportional height or width for an image, or simplify its aspect ratio, from two known dimensions.
Your results
Calculation breakdown
- Proportional height
- new width × (original height ÷ original width)
- Simplified ratio
- width ÷ GCD : height ÷ GCD
Worked example
Resizing a 1920x1080 image to a width of 1280 px gives a proportional height of 720 px, keeping the 16:9 ratio.
Assumptions
- Assumes uniform scaling with no cropping.
- Height is rounded to the nearest whole pixel.
How this calculator works
Enter an original width and height plus a new width to get the proportional new height (or vice versa), and see the simplified aspect ratio such as 16:9 or 4:3.
Frequently asked questions
How is the simplified ratio found?
The width and height are divided by their greatest common divisor to give the smallest whole-number ratio, such as 16:9.
Can I resize by height instead of width?
Yes, use the resize-by-height mode to keep the same proportions when only the target height is known.
Why keep the aspect ratio the same?
Changing width and height by different factors distorts the image, stretching or squashing the content.
Editorial review and responsibility
Reviewed by the CalcAussie editorial team on 21 September 2026. Review scope: Method, Australian terminology, material assumptions, source links and user-facing limitations.
Calculator results remain estimates based on the figures entered. Check material decisions against current official information and report a suspected error so it can be reproduced and corrected.