A JavaScript library for arbitrary-precision decimal and non-decimal arithmetic
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Latest commit d50c448 Jan 27, 2018
MikeMcl committed Jan 27, 2018 Correct base range in README



A JavaScript library for arbitrary-precision decimal and non-decimal arithmetic.

Build Status


  • Integers and decimals
  • Simple API but full-featured
  • Faster, smaller, and perhaps easier to use than JavaScript versions of Java's BigDecimal
  • 8 KB minified and gzipped
  • Replicates the toExponential, toFixed, toPrecision and toString methods of JavaScript's Number type
  • Includes a toFraction and a correctly-rounded squareRoot method
  • Supports cryptographically-secure pseudo-random number generation
  • No dependencies
  • Wide platform compatibility: uses JavaScript 1.5 (ECMAScript 3) features only
  • Comprehensive documentation and test set


If a smaller and simpler library is required see big.js. It's less than half the size but only works with decimal numbers and only has half the methods. It also does not allow NaN or Infinity, or have the configuration options of this library.

See also decimal.js, which among other things adds support for non-integer powers, and performs all operations to a specified number of significant digits.


The library is the single JavaScript file bignumber.js (or minified, bignumber.min.js).


<script src='path/to/bignumber.js'></script>


$ npm install --save bignumber.js
var BigNumber = require('bignumber.js');

ES6 module (bignumber.mjs):

//import BigNumber from 'bignumber.js';
import {BigNumber} from 'bignumber.js';

AMD loader libraries such as requireJS:

require(['bignumber'], function(BigNumber) {
    // Use BigNumber here in local scope. No global BigNumber.


In all examples below, var, semicolons and toString calls are not shown. If a commented-out value is in quotes it means toString has been called on the preceding expression.

The library exports a single function: BigNumber, the constructor of BigNumber instances.

It accepts a value of type number (up to 15 significant digits only), string or BigNumber object,

x = new BigNumber(123.4567)
y = BigNumber('123456.7e-3')
z = new BigNumber(x)
x.isEqualTo(y) && y.isEqualTo(z) && x.isEqualTo(z)      // true

and a base from 2 to 36 can be specified (higher bases can also be used if a custom alphabet is provided).

x = new BigNumber(1011, 2)          // "11"
y = new BigNumber('zz.9', 36)       // "1295.25"
z = x.plus(y)                       // "1306.25"

A BigNumber is immutable in the sense that it is not changed by its methods.

0.3 - 0.1                           // 0.19999999999999998
x = new BigNumber(0.3)
x.minus(0.1)                        // "0.2"
x                                   // "0.3"

The methods that return a BigNumber can be chained.


Some of the longer method names have a shorter alias.

x.squareRoot().dividedBy(y).exponentiatedBy(3).isEqualTo( x.sqrt().div(y).pow(3) )    // true
x.modulo(y).multipliedBy(z).eq( x.mod(y).times(z) )                                   // true

Like JavaScript's Number type, there are toExponential, toFixed and toPrecision methods

x = new BigNumber(255.5)
x.toExponential(5)                  // "2.55500e+2"
x.toFixed(5)                        // "255.50000"
x.toPrecision(5)                    // "255.50"
x.toNumber()                        // 255.5

and a base can be specified for toString.

x.toString(16)                     // "ff.8"

There is also a toFormat method which may be useful for internationalisation

y = new BigNumber('1234567.898765')
y.toFormat(2)                       // "1,234,567.90"

The maximum number of decimal places of the result of an operation involving division (i.e. a division, square root, base conversion or negative power operation) is set using the config method of the BigNumber constructor.

The other arithmetic operations always give the exact result.

BigNumber.config({ DECIMAL_PLACES: 10, ROUNDING_MODE: 4 })

x = new BigNumber(2);
y = new BigNumber(3);
z = x.dividedBy(y)                        // "0.6666666667"
z.squareRoot()                            // "0.8164965809"
z.exponentiatedBy(-3)                     // "3.3749999995"
z.toString(2)                             // "0.1010101011"
z.multipliedBy(z)                         // "0.44444444448888888889"
z.multipliedBy(z).decimalPlaces(10)       // "0.4444444445"

There is a toFraction method with an optional maximum denominator argument

y = new BigNumber(355)
pi = y.dividedBy(113)               // "3.1415929204"
pi.toFraction()                     // [ "7853982301", "2500000000" ]
pi.toFraction(1000)                 // [ "355", "113" ]

and isNaN and isFinite methods, as NaN and Infinity are valid BigNumber values.

x = new BigNumber(NaN)                                           // "NaN"
y = new BigNumber(Infinity)                                      // "Infinity"
x.isNaN() && !y.isNaN() && !x.isFinite() && !y.isFinite()        // true

The value of a BigNumber is stored in a decimal floating point format in terms of a coefficient, exponent and sign.

x = new BigNumber(-123.456);
x.c                                 // [ 123, 45600000000000 ]  coefficient (i.e. significand)
x.e                                 // 2                        exponent
x.s                                 // -1                       sign

For advanced usage, multiple BigNumber constructors can be created, each with their own independent configuration which applies to all BigNumber's created from it.

// Set DECIMAL_PLACES for the original BigNumber constructor
BigNumber.config({ DECIMAL_PLACES: 10 })

// Create another BigNumber constructor, optionally passing in a configuration object
BN = BigNumber.clone({ DECIMAL_PLACES: 5 })

x = new BigNumber(1)
y = new BN(1)

x.div(3)                            // '0.3333333333'
y.div(3)                            // '0.33333'

For futher information see the API reference in the doc directory.


The test/modules directory contains the test scripts for each method.

The tests can be run with Node.js or a browser. For Node.js use

$ npm test


$ node test/test

To test a single method, use, for example

$ node test/methods/toFraction

For the browser, open test/test.html.


See the README in the perf directory.


For Node, if uglify-js is installed

npm install uglify-js -g


npm run build

will create bignumber.min.js.

A source map will also be created in the root directory.


Open an issue, or email




The MIT Licence.