Aspect Ratio Calculator
Resize without distortion. Enter the original dimensions and one new dimension to find the other — or enter any width and height to reduce them to their simplest ratio like 16:9.
How to use this calculator
- Enter the original width and height.
- Enter one new dimension and tell the calculator whether it's a width or a height.
- Press Calculate for the matching dimension and the simplified ratio.
Formula used
Keeping the ratio constant means the fraction width/height never changes. The simplified ratio comes from dividing both dimensions by their greatest common divisor — 1920/1080 both divide by 120, giving 16:9.
Example calculation
Scaling 1920×1080 to a width of 1280: new height = 1280 × (1080/1920) = 720. So 1280×720 — same 16:9 shape, no distortion.
Both resolutions reduce to 16:9 because 1920÷120 = 16 and 1080÷120 = 9.
Aspect ratios in practice
Aspect ratio is shape independent of size: 16:9 (modern video and displays), 4:3 (older screens and many photos), 1:1 (square social posts), 21:9 (ultrawide). Any resize that changes the ratio stretches or squashes the image — the visible distortion that makes faces look wrong.
The calculator does two jobs that come up constantly: solving the partner dimension when you're resizing to a target width or height, and reverse-engineering the ratio of arbitrary dimensions so you can match crops, video exports and CSS aspect-ratio boxes precisely.
Why use this calculator?
- Resize images and video to a target size without distortion.
- Identify what ratio arbitrary dimensions actually are.
- Match export and container sizes across design, video and CSS.
Frequently asked questions
What is 16:9 in pixels?
16:9 is a shape, not a fixed size — common resolutions include 1920×1080, 1280×720, 2560×1440 and 3840×2160 (4K). All reduce to 16:9. Multiply by any factor and the ratio holds.
How do I find the aspect ratio of my image?
Enter its width and height and read the simplified ratio. The calculator divides both by their greatest common divisor — e.g. 1500×1000 reduces to 3:2, a classic photo ratio.
Why does my resized image look stretched?
The new dimensions don't match the original ratio. Solve for the correct partner dimension here rather than typing both by hand — forcing 1920×1080 content into a 1000×1000 square is what causes the squash.