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lanqy/bytesToSize.js

Created March 19, 2013 03:05
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JavaScript To Convert Bytes To MB, KB, Etc
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bytesToSize.js
// from http://scratch99.com/web-development/javascript/convert-bytes-to-mb-kb/
function bytesToSize(bytes) {
var sizes = ['Bytes', 'KB', 'MB', 'GB', 'TB'];
if (bytes == 0) return 'n/a';
var i = parseInt(Math.floor(Math.log(bytes) / Math.log(1024)));
if (i == 0) return bytes + ' ' + sizes[i];
return (bytes / Math.pow(1024, i)).toFixed(1) + ' ' + sizes[i];
};
@flycran
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flycran commented Mar 15, 2026

If you find yourself tweaking this snippet frequently, smart-unit might be worth a look — it handles this out of the box with configurable decimal places, TypeScript support, and bidirectional format/parse:

const size = new SmartUnit(['B', 'KB', 'MB', 'GB', 'TB'], { baseDigit: 1024 });
size.format(1234);    // "1.21KB"
size.parse('1.5GB'); // 1610612736

And bytes formatting is just one use case — the same API works for any unit system with variable ratios, like time, length, frequency, or anything custom:

const time = new SmartUnit(['ms', 1000, 's', 60, 'm', 60, 'h']);
time.format(5400000); // "1.5h"

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