Calculate in either direction
Start with width to find height, or start with height to find width.
Aspect Ratio Calculator
Enter an image or video ratio and one known dimension to calculate the other side, simplify the ratio, and copy its CSS aspect-ratio value.
Calculated in your browserWidth or height inputCopyable result
Calculate image and video dimensions
Choose the known side and enter its pixel size. The other side updates with the selected rounding rule.
Calculated result
1,920 × 1,080 · 16:9
Output size
1,920 × 1,080 px
- Simplified ratio
- 16:9
- Width as a percentage of height
- 177.7778%
- CSS ratio
- aspect-ratio: 16 / 9;
Calculation boundaries you can see
Rounding stays explicit
When the exact value has decimals, the result shows whether it was rounded to nearest, down, or up.
One owner for common ratios
Handle 1:1, 3:4, 4:5, 9:16, 16:9, and 21:9 in the same calculator.
Common dimension workflows
Plan before image compression
Calculate the intended dimensions before setting a maximum image edge.
Video canvases and thumbnails
Calculate landscape, vertical, or ultrawide export dimensions.
Product and portrait images
Check square or 4:5 dimensions for product and content assets.
Responsive CSS containers
Copy the simplified CSS aspect-ratio value into a web layout.
How aspect-ratio calculation works
- 1
Enter or choose a ratio
Set the ratio width and height, or choose a common preset.
- 2
Choose the known side
Select whether width or height is known, then enter its pixel value.
- 3
Review and copy
Check the other side, exact value, and rounded result before copying the dimensions.
Frequently asked questions
What is an aspect ratio?
An aspect ratio describes the relationship between width and height. A 16:9 ratio means 16 units of width for every 9 units of height, not one fixed pixel size.
How do I calculate height from width?
Choose “Width is known,” then enter the ratio and width. Height is width × ratio height ÷ ratio width.
Why does the result need rounding?
Pixel dimensions usually need whole numbers. When a ratio does not divide evenly, choose nearest, down, or up while keeping the exact value visible.
Does this tool resize my image?
No. It calculates and previews dimensions without reading, uploading, or resampling an image.
When should I use 16:9, 4:5, or 9:16?
They represent common widescreen, portrait-photo, and vertical-canvas shapes. Platform requirements can change, so check the current specification for your destination.