JavaScript Number.toPrecision()

toPrecision(precision) formats a Number to a specified number of significant digits. It returns a string and may use fixed-point or exponential notation.

const value = 1445.32678;
console.log(value.toPrecision(6)); // "1445.33"

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toPrecision() syntax Top ↑

number.toPrecision(precision)

If precision is omitted, the method behaves similarly to converting the Number to a string without forcing a specific count of significant digits.

Precision means significant digits Top ↑

console.log((11.257).toPrecision(2)); // "11"
console.log((11.257).toPrecision(5)); // "11.257"
console.log((1.1257).toPrecision(3)); // "1.13"

toPrecision() returns a string Top ↑

The older version of this tutorial treated the returned value as a number. That is incorrect: the formatted result is a string.

const result = (1445.32678).toPrecision(6);
console.log(result);        // "1445.33"
console.log(typeof result); // "string"

Trailing zeros can be significant Top ↑

console.log((11.257).toPrecision(6)); // "11.2570"

The trailing zero is part of the formatted string because six significant digits were requested.

When toPrecision() uses scientific notation Top ↑

console.log((11257).toPrecision(3)); // "1.13e+4"
console.log((11257).toPrecision(2)); // "1.1e+4"

Valid precision range Top ↑

When supplied, precision must be between 1 and 100. Values outside the supported range throw a RangeError.

try {
  (12.34).toPrecision(0);
} catch (error) {
  console.log(error.name); // RangeError
}

toPrecision() vs toFixed() Top ↑

const value = 12.3456;
console.log(value.toFixed(2));      // "12.35" - 2 decimal places
console.log(value.toPrecision(2));  // "12" - 2 significant digits

See toFixed() when you need a fixed count of decimal places.

Convert text input before formatting Top ↑

Methods such as toPrecision() belong to Number values. Convert and validate text before using them.

const value = parseFloat("1445.32678");
if (!Number.isNaN(value)) {
  console.log(value.toPrecision(6));
}

Related conversion pages: parseInt(), parseFloat(), and NaN checks.

Related tutorials Top ↑

Also review Math.ceil(), Math.floor(), and toFixed().

← JavaScript Math Reference

Subhendu Mohapatra

Author & Instructor at plus2net

I write and maintain practical tutorials on Python, PHP, SQL, JavaScript, HTML, jQuery, and web development at plus2net. The tutorials focus on clear explanations, working examples, and code that readers can test and adapt while learning.

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