JavaScript Number parseFloat() Method

What You’ll Learn

Number.parseFloat() is a static method on Number (same API as MDN Number.parseFloat). Call Number.parseFloat(string) — not on a number instance. It turns text into a floating-point number and keeps decimals. This tutorial covers syntax, junk suffixes, scientific notation, five examples, and try-it labs.

Introduction

Prices, ratings, and CSS lengths often arrive as text — "3.14", "19.99", or "4.5rem". Number.parseFloat() reads the leading floating-point number from that text.

It is the same function as the global parseFloat ((Number.parseFloat === parseFloat). The Number. form keeps number helpers together on one object.

This page is part of JavaScript Number Methods. Related tools include Number.parseInt() for integers, toFixed() for display decimals, and Number.isNaN() to check failed parses.

Understanding the parseFloat() Method

Call Number.parseFloat(string). The engine:

• Coerces the argument to a string and skips leading whitespace.
• Reads an optional sign, digits, optional decimal point, and optional exponent (e / E).
• Stops at the first character that is not part of that float (so "3.14px" still yields 3.14).
• Returns NaN if the first non-whitespace character cannot start a number.

📝 Syntax

General form of the static method Number.parseFloat:

Number.parseFloat(string)

Parameters

• string (any) — value to parse (coerced to string). Leading whitespace is ignored.

Return value

A floating-point number, or NaN:

Exceptions

• None for normal calls — bad input yields NaN rather than a thrown error.

Common patterns

Number.parseFloat("3.14");              // 3.14
Number.parseFloat("3.14px");            // 3.14
Number.parseFloat("1.23e+2");           // 123
Number.parseFloat("4.567abcdefgh");     // 4.567
Number.parseFloat("hello");             // NaN
Number.parseFloat === parseFloat;       // true

Examples Gallery

Examples follow MDN / parseFloat patterns. Use View Output or Try It Yourself for each case.

Number.parseFloat("3.14");  // 3.14

3.14

Number.parseFloat("3.14px");  // 3.14

3.14

Number.parseFloat("1.23e+2");  // 123

123

function circumference(r) {
  if (Number.isNaN(Number.parseFloat(r))) {
    return 0;
  }
  return Number.parseFloat(r) * 2.0 * Math.PI;
}

circumference("4.567abcdefgh");  // ≈ 28.695307297889173

28.695307297889173

Number.parseFloat("hello");  // NaN

NaN

🚀 Common Use Cases

• Form inputs — prices, ratings, and measurements typed as text.
• CSS / DOM sizes — pull the float out of "1.5rem" or "12.5px".
• Science / sensors — read values that may include scientific notation.
• Tolerant parsers — accept trailing units or labels without failing.
• Guarded math — check Number.isNaN before multiplying (MDN circumference pattern).
• Not for bases — use Number.parseInt when radix 2–36 matters.

📝 Notes

• This is a static method — use Number.parseFloat(s) only.
• Number.parseFloat === parseFloat — same built-in function.
• There is no radix parameter — unlike Number.parseInt.
• Keeps the fractional part: Number.parseFloat("15.9") is 15.9.
• Accepts scientific notation such as "1.5e3".
• Check failures with Number.isNaN(), not === NaN.

💡 Best Practices