About the Aspect Ratio Calculator
Aspect ratio is the quiet cause of letterboxed video, squashed thumbnails and hero images that crop badly on mobile. Enter any width and height and this calculator reduces it to its simplest ratio, gives you the decimal and percentage forms used in CSS padding tricks, and scales the pair to a new target width without distortion.
How to use it
- 01Enter the original width and height in pixels.
- 02Enter the width you want to scale to.
- 03Read the simplified ratio, decimal ratio, padding percentage and the matching scaled height.
- 04Use the swap button to flip landscape and portrait orientations.
Features
- Greatest-common-divisor reduction to the simplest whole-number ratio
- Decimal ratio to four places for layout maths
- Height-over-width percentage for aspect-ratio padding boxes
- Proportional height for any target width, rounded to the nearest pixel
- Megapixel figure for judging image weight
Practical examples
Checking a video export
1920 × 1080 reduces to 16:9 with a 56.25% padding value — the number behind the classic responsive video wrapper.
Resizing a hero image
An original of 2400 × 1500 scaled to a 1280 target width gives 1280 × 800, so the crop stays identical at the smaller size.
Limitations
- Scaled heights are rounded to whole pixels, so very small targets can drift by half a pixel from the exact ratio.
- The calculator works on numbers only; it does not open or resize an actual image file.
Privacy
Only two numbers are involved and they never leave the page. Nothing is stored or transmitted.
Read the full privacy policy for how the site as a whole handles data.
Frequently asked questions
What is the percentage value for?
It is the height divided by the width. Used as bottom padding on a wrapper element, it reserves exactly the right space for a responsive embed.
Why does my ratio look unusual, like 683:384?
That means the two numbers share no tidy common factor. It is usually a sign the source dimensions were already rounded somewhere upstream.
Can I use it for print sizes?
Yes. The maths is unit-agnostic, so millimetres or inches work as long as both fields use the same unit.