16:9 · 4:5 · 9:16
Scale dimensions without squashing anything
Give it the original size and one new measurement, and it returns the other. Simple arithmetic that is remarkably easy to get wrong when you are in a hurry.
Processed on your own hardware · never transmitted, never stored
Stretching is obvious even when nobody can name it
Every video has a fixed relationship between its width and its height. Change one without moving the other in step and faces widen, circles turn oval, and viewers register that something is wrong long before they work out what.
The maths is trivial and still gets fumbled, particularly with unusual sources. A recording of a laptop display might be 2880 by 1800, which is sixteen by ten rather than sixteen by nine. A clip cropped in a phone app can end up at a ratio nobody planned and nobody wrote down.
This also flags something most calculators ignore entirely: H.264 requires both dimensions to be even numbers. An odd result gets silently adjusted by the encoder, which can shift your framing by a pixel and occasionally produce a green line down one edge.
Scaling and reshaping are different problems
This calculator scales — it keeps the same shape at a different size. Turning sixteen by nine footage into a square is not scaling at all: it requires either cutting the sides away or adding bars, and that is a decision about what the viewer sees rather than a calculation. No arithmetic can make a rectangle into a square without losing or inventing something.
Common questions
What does 16:9 mean?
For every sixteen units of width there are nine of height. Both 1920x1080 and 1280x720 are 16:9, which is why one scales cleanly into the other.
Why must both numbers be even?
H.264 stores colour information in two by two pixel blocks, so odd dimensions cannot divide cleanly.
Can I change the shape without distortion?
Only by cropping or padding. Something has to be removed or added.
What ratio is my screen recording?
Frequently 16:10 rather than 16:9, since many laptop displays are 16:10. Enter the recorded numbers and the reduced ratio is shown.