Practical guide · dimensions explained
Aspect ratios, resizing and exact pixel crops
Reduce a ratio, calculate a proportional resize, and choose a centered crop without mixing these operations.
Reviewed September 28, 2026 · Worked examples calculated for this guide
Illustration of the related tool’s example; proportions only.
Reduce width and height together
A ratio describes shape, with width first. Divide both pixel dimensions by their greatest common divisor. The 1920 × 1080 pair reduces to 16:9; 2400 × 3000 reduces to 4:5. Reversing 4:5 to 5:4 changes a portrait shape into a landscape shape. It is not just another way to write the same ratio.
Resize the full image
To resize 1920 × 1080 to a width of 1280, multiply both dimensions by 1280 ÷ 1920. The result is exactly 1280 × 720. A width of 1000 instead gives an exact height of 562.5, which must round to a whole pixel: 563 in our calculator. The small resulting ratio difference is shown explicitly. The calculator supplies dimensions; use an editor to resample the actual file.
Crop to a new shape
For a 3000 × 2000 source and an exact 4:5 crop, the largest whole-pixel rectangle is 1600 × 2000. A centered crop begins at x = 700 and y = 0, measured from the source’s upper-left. It retains about 53.33% of the source area. Unlike a resize, this changes what remains visible.
Understand integer and centering limits
An exact a:b crop must be an integer multiple of the reduced ratio. For very small images, a requested ratio may not fit at all. If centering leaves an odd number of pixels to remove, the extra pixel is removed from the right or bottom. We report integer coordinates and an exact ratio; an editor that uses fractional crop boundaries may make a slightly different choice.