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A small, fast JavaScript library for arbitrary-precision decimal arithmetic.

npm version npm downloads


  • Simple API
  • Faster, smaller and easier-to-use than JavaScript versions of Java's BigDecimal
  • Only 6 KB minified
  • Replicates the toExponential, toFixed and toPrecision methods of JavaScript Numbers
  • Stores values in an accessible decimal floating point format
  • Comprehensive documentation and test set
  • No dependencies
  • Uses ECMAScript 3 only, so works in all browsers

The little sister to bignumber.js and decimal.js. See here for some notes on the difference between them.


The library is the single JavaScript file big.js or the ES module big.mjs.


Add Big to global scope:

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

ES module:

<script type='module'>
import Big from './path/to/big.mjs';

Get a minified version from a CDN:

<script src=''></script>


$ npm install big.js


const Big = require('big.js');

ES module:

import Big from 'big.js';


import Big from '';
import Big from '';


In the code examples below, semicolons and toString calls are not shown.

The library exports a single constructor function, Big.

A Big number is created from a primitive number, string, or other Big number.

x = new Big(123.4567)
y = Big('123456.7e-3')                 // 'new' is optional
z = new Big(x)
x.eq(y) && x.eq(z) && y.eq(z)          // true

In Big strict mode, creating a Big number from a primitive number is disallowed.

Big.strict = true
x = new Big(1)                         // TypeError: [big.js] Invalid number
y = new Big('1.0000000000000001')
y.toNumber()                           // Error: [big.js] Imprecise conversion

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

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

The methods that return a Big number can be chained.

x.sqrt().div(y).pow(3).gt(y.mod(z))    // true

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

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

The arithmetic methods always return the exact result except div, sqrt and pow (with negative exponent), as these methods involve division.

The maximum number of decimal places and the rounding mode used to round the results of these methods is determined by the value of the DP and RM properties of the Big number constructor.

Big.DP = 10
Big.RM = Big.roundHalfUp

x = new Big(2);
y = new Big(3);
z = x.div(y)                           // "0.6666666667"
z.sqrt()                               // "0.8164965809"
z.pow(-3)                              // "3.3749999995"
z.times(z)                             // "0.44444444448888888889"
z.times(z).round(10)                   // "0.4444444445"

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

x = new Big(-123.456);
x.c                                    // [1,2,3,4,5,6]    coefficient (i.e. significand)
x.e                                    // 2                exponent
x.s                                    // -1               sign

For advanced usage, multiple Big number constructors can be created, each with an independent configuration.

For further information see the API reference documentation.


To minify using, for example, npm and terser

$ npm install -g terser
$ terser big.js -c -m -o big.min.js


The test directory contains the test scripts for each Big number method.

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

Run all the tests:

$ npm test

Test a single method:

$ node test/toFixed

For the browser, see runner.html and test.html in the test/browser directory.

big-vs-number.html is a old application that enables some of the methods of big.js to be compared with those of JavaScript's Number type.


The DefinitelyTyped project has a Typescript type definitions file for big.js.

$ npm install --save-dev @types/big.js

Any questions about the TypeScript type definitions file should be addressed to the DefinitelyTyped project.




Financial supporters

Thank you to all who have supported this project via Open Collective, particularly Coinbase.