Aspect Ratio Calculator

How to use the Aspect Ratio Calculator

Enter an original width and height to simplify the ratio, then fix either a new width or height and calculate the matching dimension.

Calculate a simplified width-to-height ratio and find a missing dimension while preserving that ratio. It helps plan responsive images, video frames, canvases, and print layouts.

The selected image is decoded and processed in the browser. Keep the original until the downloaded output has been opened and checked on the target device.

1. Enter the original pixel width and height.
2. Fieldlet reduces those dimensions using their greatest common divisor.
3. Choose whether the new width or height is known, then enter it to calculate the proportional missing dimension.

Last reviewed for accuracy: 2026-09-01

Worked examples

How the result is produced

A ratio compares width with height after removing their greatest common divisor. To preserve it, scale both dimensions by the same factor or solve the cross-multiplication equation.

• Ratio width:height = width ÷ common divisor : height ÷ common divisor
• New height = new width × original height ÷ original width
• Rounding to whole pixels can introduce a tiny ratio difference

Solve from width or from height

Choose which new dimension is known, then Fieldlet calculates the other from the original ratio. The computed result is rounded to a whole pixel, so very small sizes can differ slightly from the exact mathematical proportion.

• Enter the original width and height first.
• Select whether the target width or height is fixed.
• Review platform crop and safe-area rules after resizing.

Limitations and common mistakes

• A matching canvas ratio does not guarantee that important content fits after cropping.
• Some platforms use display aspect ratio, pixel aspect ratio, or safe areas with additional rules.

Common questions