Aspect ratio calculator

How to use this tool

1. Enter the original width and height as positive integers.
2. Choose whether the target fixes width or height, then enter its length.
3. Inspect the matching size, reduced ratio and width/height scale factors.

Fit a 16:9 image to 800 px width

Input and settings

1920 × 1080; resize by width; target 800

Result

800 × 450 px; ratio 16:9

This tool calculates dimensions. Use Resize image to change an actual file.

A ratio is not a resolution

1920×1080 and 1280×720 contain different pixel counts but share a 16:9 ratio. Dividing the two dimensions by their greatest common divisor produces the reduced integer ratio. Portrait video simply uses a height larger than its width.

Swap inputs reverses width and height, making it easy to compare 16:9 with 9:16. This does not rotate or crop a source file; it keeps dimension arithmetic separate from image editing.

Integer pixels can change a ratio slightly

The matching dimension is rounded to the nearest whole pixel, with a minimum of 1 px. Very small targets or extreme proportions can produce different width and height scale factors, so the relative ratio difference is displayed explicitly.

Original and target dimensions are bounded to one million. The schematic is adjusted for legibility; it does not predict the sharpness, resampling method or file size of an exported image.

Common questions