Aspect Ratio Calculator

What this generator does

Divides the width and height by their greatest common factor to get the ratio in its simplest form, names it where it is a familiar one, and scales it to a width or height you choose.

How to use this tool

1. Enter the width and height you have.
2. Read the reduced ratio and its decimal form.
3. Enter a target width or height to get the other one.
4. Common ratios are named where the numbers match one.

Understanding the controls

Width and height

Whole numbers in any unit — pixels, millimetres, anything, as long as both are the same.

Scale to this width

The size you want to resize to. The matching dimension is worked out from the reduced ratio, rounded to a whole number.

Common use cases

• Resizing an image or a video without distorting it
• Checking what ratio a set of dimensions actually is
• Working out a height for a given width in a layout
• Choosing a canvas size that matches a target format
• Confirming a video is genuinely widescreen

How this generator works

The reduced ratio is confirmed to have no common factor left, and to describe the same shape as the numbers that went in — the decimal is compared either way. Scaling back out to the original width must then return the original height, which catches a rounding mistake in the scaling arithmetic.

Randomness and fairness

Nothing is random. The same dimensions always give the same ratio.

For how randomness is produced across the whole site, see how Generate Random works.

Limitations and good to know

• Whole numbers only, so a size given in decimals must be rounded before it goes in.
• Scaled dimensions are rounded to the nearest whole number, which can be a pixel out from an exact ratio.
• Common ratios are named from a short list; an uncommon one is simply given as its reduced form.
• Pixel aspect ratio, as distinct from display aspect ratio, is not considered.

Privacy and your data

The arithmetic runs in your browser. Nothing you enter is transmitted or stored.