Aspect Ratio Calculator
How it worksHow to calculate aspect ratio
Enter the original pixel width and height to find their simplest ratio. To resize, choose a target width or height; the other side follows the same proportion. Or start with a ratio and one known side.
For whole numbers, divide both dimensions by their greatest common divisor. For decimal inputs, first multiply both by the same power of ten to make them whole numbers, then simplify.
New height = new width × original height ÷ original width
New width = new height × original width ÷ original height
For a diagonal D and ratio A:B, width = D × A ÷ √(A² + B²), and height = D × B ÷ √(A² + B²). The decimal ratio is width ÷ height. Total pixels are width × height; diagonal is √(width² + height²).
Common ratios, or your own
Choose 16:9, 9:16, 4:3, 3:2, 1:1, 21:9 and additional cinema, portrait and display ratios. Custom positive ratios work too. Resolution presets populate actual dimensions; the ratio is always calculated from those dimensions.
For example, 2560 × 1080 simplifies to 64:27, not exactly 21:9. The nearest listed ratio uses the smallest absolute difference between decimal ratios; it does not replace your exact ratio.
Whole-pixel and even-pixel rounding can slightly change the output shape. The calculator shows the resulting ratio when that happens. Decimal results are displayed to six places; calculations retain browser numeric precision.
Preset references: Andrew Hedges, mononodes, CalculatorSoup Omni Calculator and Digital Rebellion.
Questions about aspect ratio
How do I use this aspect ratio calc?
Choose original dimensions to simplify a resolution and resize it. Choose a ratio and a known side when you already know the proportions. Results update as you type, and Copy result copies the current calculation.
Is changing the ratio the same as resizing an image?
No. This tool calculates dimensions; it does not edit image files. Proportional resizing keeps the original ratio. Fitting a different ratio requires cropping, padding or distortion in an image editor.
Are there usage or input limits?
There is no daily calculation limit. Each input must be greater than zero and no more than 1,000,000,000, with up to six decimal places. Calculated dimensions must stay within the same range. This page handles one calculation at a time and does not save history.