Aspect Ratio Calculator

Keeping the shape

An aspect ratio is just the relationship between width and height. Scaling while keeping that relationship is one multiplication: new height equals new width times the original height divided by the original width. Get it wrong in either direction and faces stretch or squash, which readers notice immediately even when they cannot say why.

Exact against familiar

Two numbers are shown because they answer different questions. The exact ratio is the arithmetic truth, reduced as far as it goes. It is often unhelpful: 1366 x 768 reduces to 683:384, which is correct and tells you nothing. The nearest common ratio names the shape people actually recognise, and says how far off it is, so you can decide whether the difference matters. In that example it is 16:9 to within a tenth of a per cent, which is why the screen was sold as widescreen.

Even numbers

Most encoders want both dimensions to be even, and some want them divisible by four. This is not fussiness: the compression works on blocks of pixels, and a frame that does not divide cleanly has to be padded. When the calculated height lands on a fraction, round to the nearest even number. A single pixel will not be noticed; a failed export will.

Cropping against letterboxing

When a video has to fit a frame of a different shape, there are two honest options and one bad one. You can crop, losing what falls outside. You can letterbox, adding bars and keeping everything. Or you can stretch, which keeps every pixel and ruins all of them. The first two are choices about what matters in the shot. The third is almost never right.

Vertical video

A 9:16 frame is not a broken 16:9 one, it is simply taller than it is wide, and the same arithmetic applies. Filming for it means composing for it: a wide shot that reads clearly in landscape usually loses its subject entirely once the sides are gone.