pretty-bytes

What is pretty-bytes?

The pretty-bytes npm package is a utility that converts bytes to a human-readable string. It takes a numeric value representing the number of bytes and returns a string with a more readable format, including the appropriate unit such as bytes, kilobytes, megabytes, etc.

What are pretty-bytes's main functionalities?

Convert bytes to a human-readable string

This feature allows you to convert a numeric value of bytes into a string that represents the size in a more understandable format, automatically choosing the right unit.

const prettyBytes = require('pretty-bytes');
console.log(prettyBytes(1024)); // '1 kB'

Convert bytes to a human-readable string with options

This feature allows you to specify options such as using binary (IEC) units instead of metric (SI) units, which changes the way the units are calculated and displayed.

const prettyBytes = require('pretty-bytes');
console.log(prettyBytes(1000, {binary: true})); // '1000 B'
console.log(prettyBytes(1024, {binary: true})); // '1 KiB'

Locale support

This feature allows you to format the number using a locale string, which affects the output by using the appropriate decimal separator and grouping for the specified locale.

const prettyBytes = require('pretty-bytes');
console.log(prettyBytes(123456789, {locale: 'de'})); // '123,5 MB'

Other packages similar to pretty-bytes

filesize

The filesize package provides similar functionality to pretty-bytes, allowing for human-readable file size strings from byte amounts. It offers additional options for customization, such as setting the number of decimal places, and has methods for partial application.

bytes

The bytes package is another alternative that formats byte sizes into human-readable strings. It supports conversion from a string with a unit back to bytes, which pretty-bytes does not do.

README

pretty-bytes

Convert bytes to a human readable string: 1337 → 1.34 kB

Useful for displaying file sizes for humans.

Note that it uses base-10 (e.g. kilobyte). Read about the difference between kilobyte and kibibyte.

Install

npm install pretty-bytes

Usage

import prettyBytes from 'pretty-bytes';

prettyBytes(1337);
//=> '1.34 kB'

prettyBytes(100);
//=> '100 B'

// Display with units of bits
prettyBytes(1337, {bits: true});
//=> '1.34 kbit'

// Display file size differences
prettyBytes(42, {signed: true});
//=> '+42 B'

// Localized output using German locale
prettyBytes(1337, {locale: 'de'});
//=> '1,34 kB'

// Fixed width for alignment (useful for progress bars and tables)
prettyBytes(1337, {fixedWidth: 8});
//=> ' 1.34 kB'

API

prettyBytes(number, options?)

number

Type: number | bigint

The number to format.

options

Type: object

signed

Type: boolean
Default: false

Include plus sign for positive numbers. If the difference is exactly zero a space character will be prepended instead for better alignment.

bits

Type: boolean
Default: false

Format the number as bits instead of bytes. This can be useful when, for example, referring to bit rate.

import prettyBytes from 'pretty-bytes';

prettyBytes(1337, {bits: true});
//=> '1.34 kbit'

binary

Type: boolean
Default: false

Format the number using the Binary Prefix instead of the SI Prefix. This can be useful for presenting memory amounts. However, this should not be used for presenting file sizes.

import prettyBytes from 'pretty-bytes';

prettyBytes(1000, {binary: true});
//=> '1000 B'

prettyBytes(1024, {binary: true});
//=> '1 KiB'

locale

Type: boolean | string | string[]
Default: false

• If false: Output won't be localized.
• If true: Localize the output using the system/browser locale.
• If string: Expects a BCP 47 language tag (For example: en, de, …)
• If string[]: Expects a list of BCP 47 language tags (For example: en, de, …)

[!IMPORTANT] Only the number and decimal separator are localized. The unit title is not and will not be localized.

minimumFractionDigits

Type: number
Default: undefined

The minimum number of fraction digits to display.

If neither minimumFractionDigits nor maximumFractionDigits is set, the default behavior is to round to 3 significant digits.

[!NOTE] When minimumFractionDigits or maximumFractionDigits is specified, values are truncated instead of rounded to provide more intuitive results for file sizes.

import prettyBytes from 'pretty-bytes';

// Show the number with at least 3 fractional digits
prettyBytes(1900, {minimumFractionDigits: 3});
//=> '1.900 kB'

prettyBytes(1900);
//=> '1.9 kB'

maximumFractionDigits

Type: number
Default: undefined

The maximum number of fraction digits to display.

If neither minimumFractionDigits nor maximumFractionDigits is set, the default behavior is to round to 3 significant digits.

[!NOTE] When minimumFractionDigits or maximumFractionDigits is specified, values are truncated instead of rounded to provide more intuitive results for file sizes.

import prettyBytes from 'pretty-bytes';

// Show the number with at most 1 fractional digit
prettyBytes(1920, {maximumFractionDigits: 1});
//=> '1.9 kB'

prettyBytes(1920);
//=> '1.92 kB'

space

Type: boolean
Default: true

Put a space between the number and unit.

import prettyBytes from 'pretty-bytes';

prettyBytes(1920, {space: false});
//=> '1.92kB'

prettyBytes(1920);
//=> '1.92 kB'

nonBreakingSpace

Type: boolean
Default: false

Use a non-breaking space instead of a regular space to prevent the unit from wrapping to a new line.

Has no effect when space is false.

fixedWidth

Type: number
Default: undefined

Pad the output to a fixed width by right-aligning it.

Useful for creating aligned columns in tables or progress bars.

If the output is longer than the specified width, no padding is applied.

Must be a non-negative integer. Throws a TypeError for invalid values.

import prettyBytes from 'pretty-bytes';

prettyBytes(1337, {fixedWidth: 10});
//=> '   1.34 kB'

prettyBytes(100_000, {fixedWidth: 10});
//=> '  100 kB'

// Useful for progress bars and tables
[1000, 10_000, 100_000].map(bytes => prettyBytes(bytes, {fixedWidth: 8}));
//=> ['   1 kB', '  10 kB', ' 100 kB']

FAQ

Why kB and not KB?

k is the standardized SI prefix for kilo.

Related

• pretty-bytes-cli - CLI for this module
• pretty-ms - Convert milliseconds to a human readable string