JavaScript library to generate a human readable String describing the file size

Usage no npm install needed!

<script type="module">
  import filesize from '';



build status downloads CDNJS version

filesize.js provides a simple way to get a human readable file size string from a number (float or integer) or string.

Optional settings

filesize() accepts an optional descriptor Object as a second argument, so you can customize the output.


(number) Number base, default is 10


(boolean) Enables bit sizes, default is false


(number) Specifies the symbol via exponent, e.g. 2 is MB for base 2, default is -1


(boolean) Enables full form of unit of measure, default is false


(array) Array of full form overrides, default is []

locale (overrides 'separator')

(string || boolean) BCP 47 language tag to specify a locale, or true to use default locale, default is ""

localeOptions (overrides 'separator', requires string for 'locale' option)

(object) Dictionary of options defined by ECMA-402 (Number.prototype.toLocaleString). Requires locale option to be explicitly passed as a string, otherwise is ignored.


(string) Output of function (array, exponent, object, or string), default is string


(boolean) Decimal place end padding, default is false


(number) Sets precision of numerical output, default is 0


(number) Decimal place, default is 2


(string) Rounding method, can be round, floor, or ceil, default is round


(string) Decimal separator character, default is .


(string) Character between the result and symbol, default is " "


(string) Standard unit of measure, can be iec or jedec, default is iec; can be overruled by base


(object) Dictionary of IEC/JEDEC symbols to replace for localization, defaults to english if no match is found


(boolean) Enables unix style human readable output, e.g ls -lh, default is false


filesize(500);                        // "500 B"
filesize(500, {bits: true});          // "4 kbit"
filesize(265318, {base: 2});          // "259.1 KiB"
filesize(265318);                     // "265.32 kB"
filesize(265318, {round: 0});         // "265 kB"
filesize(265318, {output: "array"});  // [265.32, "kB"]
filesize(265318, {output: "object"}); // {value: 265.32, symbol: "kB", exponent: 1, unit: "kB"}
filesize(1, {symbols: {B: "Б"}});     // "1 Б"
filesize(1024);                       // "1.02 kB"
filesize(1024, {exponent: 0});        // "1024 B"
filesize(1024, {output: "exponent"}); // 1
filesize(265318, {standard: "jedec"});  // "259.1 KB"
filesize(265318, {base: 2, fullform: true}); // "259.1 kibibytes"
filesize(12, {fullform: true, fullforms: ["байтов"]});  // "12 байтов"
filesize(265318, {separator: ","});   // "265,32 kB"
filesize(265318, {locale: "de"});   // "265,32 kB"

Partial Application

filesize.partial() takes the second parameter of filesize() and returns a new function with the configuration applied upon execution. This can be used to reduce Object creation if you call filesize() without caching the descriptor in lexical scope.

const size = filesize.partial({base: 2, standard: "jedec"});

size(265318); // "259.1 KB"

How can I load filesize.js?

filesize.js supports AMD loaders (require.js, curl.js, etc.), node.js & npm (npm install filesize), or using a script tag.

An ES6 version is bundled with an npm install, but requires you load it with the full path, e.g. require(path.join(__dirname, 'node_modules', 'filesize', 'lib', 'filesize.es6.js')).


Copyright (c) 2021 Jason Mulligan Licensed under the BSD-3 license.