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.

The toPrecision() method of Number values returns a string representing this number to the specified number of significant digits.

Try it

Syntax

js
toPrecision()
toPrecision(precision)

Parameters

precision Optional

An integer specifying the number of significant digits.

TypeError

Thrown if this method is invoked on an object that is not a Number.

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 to precision or less than -6. Has the same behavior as Number.prototype.toString() if the precision argument is omitted.

Exceptions

RangeError

Thrown if precision is not between 1 and 100 (inclusive).

Examples

Using toPrecision

js
// This number has exponent 0, so it will never use exponential notation
let 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 notation
num = 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 4
num = 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 notation
num = 0.00000012345;
console.log(num.toPrecision(1)); // '1e-7'
console.log(num.toPrecision(10)); // '1.234500000e-7'

Specifications

Specification
ECMAScript Language Specification
# sec-number.prototype.toprecision

Browser compatibility

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See also