The source dimensions are 1920 wide by 1080 high. The target width is fixed at 1280, so height is the only unknown. This example needs no rounding because the proportional result is already a whole number.

Reduce the source ratio

The greatest common divisor of 1920 and 1080 is 120. Dividing both values by 120 gives 16:9. The target must keep width divided by height equal to 16 divided by 9.

Calculate the target height

Target height = 1280 × 1080 ÷ 1920 = 720. Using the reduced terms gives the same calculation: 1280 × 9 ÷ 16 = 720. The unrounded missing dimension is exactly 720.

Copy 1280 × 720

The proportional pair is 1280 × 720. Nearest, ceiling, and floor all return 720 because the missing dimension has no fractional part. Copying the pair records the numeric result; AspectFit does not create or change an image.