Resize an image without stretching: solve the missing dimension
Keeping the width-to-height ratio preserves shape. You only need the old ratio and one new dimension to calculate the other.
Ratio calculator →Keep the order consistent
For a 16:9 width-to-height ratio and new width 1280 pixels, set a=16, b=9 and c=1280. The tool calculates d=b×c/a = 720 pixels. Thus the new size is 1280×720. If the known new measurement is height rather than width, reverse the ratio order so that c corresponds to the same kind of dimension as a.
Distinguish resize from crop
Proportional resizing changes both dimensions by the same multiplier. Cropping removes content, while stretching uses different multipliers and changes shape. A target box whose ratio differs from the original cannot be filled perfectly without cropping, stretching or leaving space. The ratio calculator gives the proportional dimension; it does not decide which visual compromise suits the design.
Handle whole pixels and resolution
A proportional calculation can return a fractional pixel count. For a 3:2 ratio and width 1000, height is 666.666… pixels; rounding to an integer introduces a small ratio difference. Check the requirements of the platform or output format. Enlarging the pixel dimensions also does not create the detail of a genuinely higher-resolution original. Preserve the source file and judge the final image at its intended viewing size. The tool assumes strictly positive dimensions; an empty or zero-width image has no useful aspect-ratio resize.
Try the calculators
- Ratio calculator
Find d in a:b = c:d from a, b and c.
- Fraction calculator
Add, subtract, multiply and divide fractions.
- Percentage calculator
Find a percentage of any number.