FREE WEB TOOL

Aspect ratio calculator

Simplify an aspect ratio and calculate matching dimensions.

Use tool

WidthHeightNew width (optional)

How to use it

Simplify width and height into an aspect ratio and, optionally, calculate the matching height for a new width.

Enter the original width and height.
Optionally enter a new width.
Select Calculate to see the simplified ratio and matching height.

Ratio: Width and height are rounded to integers, then reduced by GCD
New height: new width × original height ÷ original width
Input: Width and height must be positive
Units: Use the same unit for width and height

1920×1080 reduces to 16:9

1920 × 1080 reduces to 16:9. A new width of 1280 gives a matching height of 720.

The ratio reduction rounds original width and height to whole numbers. It is intended for ordinary pixel/dimension work rather than exact fractional geometry.

Greatest common divisor creates the reduced ratio

Both dimensions are divided by their GCD so a large pair such as 1920:1080 becomes easier to recognize.

The optional calculation is width-driven

You supply the new width and the tool returns the proportional height. It does not provide a separate target-height field.

Same ratio does not mean same resolution

1920×1080 and 1280×720 share 16:9 but contain different pixel counts.

Zero and negative dimensions are invalid

A ratio or resize calculation needs positive dimensions, so those values are rejected instead of producing NaN or infinity.

Related references: DPI, PPI & px · Paper sizes · Aspect ratios