Nearest Normal Ratio Calculator

README.md

Nearest Normal Aspect Ratio

This function returns the nearest aspect ratio of a width and height within a limited range of possible aspect ratios.

In other words, while 649x360 technically has an aspect ratio of 649:360, it’s often useful to know that the nearest normal aspect ratio is actually 9:5 (648x360).

nearestNormalAspectRatio(width, height, [side], [maxWidth], [maxHeight])

• width: The width of the space.
• height: The height of the space.
• side: The nearest ratio to side with. A number higher than zero tells the function to always return the nearest ratio that is equal or higher than the actual ratio, whereas a smaller number returns the nearest ratio higher that is equal or smaller than the actual ratio. Defaults to 0.
• maxWidth: The maximum width in the nearest normal aspect ratio. Defaults to 16.
• maxWidth: The maximum height in the nearest normal aspect ratio. Defaults to 16.

closestAspectRatio.js

function nearestNormalAspectRatio(width, height, side) {
	var
	ratio = (width * 100) / (height * 100),
	maxW = 3 in arguments ? arguments[2] : 16,
	maxH = 4 in arguments ? arguments[3] : 16,
	ratiosW = new Array(maxW).join(',').split(','),
	ratiosH = new Array(maxH).join(',').split(','),
	ratiosT = {},
	ratios = {},
	match,
	key;

	ratiosW.forEach(function (empty, ratioW) {
		++ratioW;

		ratiosH.forEach(function (empty, ratioH) {
			++ratioH;

			ratioX = (ratioW * 100) / (ratioH * 100);

			if (!ratiosT[ratioX]) {
				ratiosT[ratioX] = true;

				ratios[ratioW + ':' + ratioH] = ratioX;
			}
		});
	});

	for (key in ratios) {
		if (!match || (
			!side && Math.abs(ratio - ratios[key]) < Math.abs(ratio - ratios[match])
		) || (
			side < 0 && ratios[key] <= ratio && Math.abs(ratio - ratios[key]) < Math.abs(ratio - ratios[match])
		) || (
			side > 0 && ratios[key] >= ratio && Math.abs(ratio - ratios[key]) < Math.abs(ratio - ratios[match])
		)) {
			match = key;
		}
	}

	return match;
}

Hey Jonathan you rock!