Number.prototype.toPrecision()
Baseline Widely available
This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.
ThetoPrecision() method ofNumber values returns a string representing this number to the specified number of significant digits.
Try it
function precise(x) { return x.toPrecision(4);}console.log(precise(123.456));// Expected output: "123.5"console.log(precise(0.004));// Expected output: "0.004000"console.log(precise(1.23e5));// Expected output: "1.230e+5"Syntax
js
toPrecision()toPrecision(precision)Parameters
precisionOptionalAn integer specifying the number of significant digits.
Return value
A string representing the given number, using the given number of significant digits. Scientific notation is used if the exponent is greater than or equal toprecision or less than -6. Has the same behavior asNumber.prototype.toString() if theprecision argument is omitted.
Exceptions
RangeErrorThrown if
precisionis not between1and100(inclusive).TypeErrorThrown if this method is invoked on an object that is not a
Number.
Examples
UsingtoPrecision
js
// This number has exponent 0, so it will never use exponential notationlet num = 5.123456;console.log(num.toPrecision()); // '5.123456'console.log(num.toPrecision(5)); // '5.1235'console.log(num.toPrecision(2)); // '5.1'console.log(num.toPrecision(1)); // '5'// This number has exponent -4, so it will never use exponential notationnum = 0.000123;console.log(num.toPrecision()); // '0.000123'console.log(num.toPrecision(5)); // '0.00012300'console.log(num.toPrecision(2)); // '0.00012'console.log(num.toPrecision(1)); // '0.0001'// This number has exponent 3, so it will use exponential notation if precision is less than 4num = 1234.5;console.log(num.toPrecision(1)); // '1e+3'console.log(num.toPrecision(2)); // '1.2e+3'console.log(num.toPrecision(6)); // '1234.50'// This number has exponent -7, so it will always use exponential notationnum = 0.00000012345;console.log(num.toPrecision(1)); // '1e-7'console.log(num.toPrecision(10)); // '1.234500000e-7'Specifications
| Specification |
|---|
| ECMAScript® 2026 Language Specification # sec-number.prototype.toprecision |