Round a Number to 3 Decimal Places in JavaScript

Round a Number to 3 Decimal Places #

Use the toFixed() method to round a number to 3 decimal places, e.g. num.toFixed(3). The toFixed method formats a number to a specified number of decimal places and rounds the number if necessary.

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const num1 = 7.456677;
const result1 = num1.toFixed(3);
console.log(result1); // 👉️ 7.457
console.log(typeof result1); // 👉️ string

// 👇️ if the value is a string
// call parseFloat to convert it to a number first
const str1 = '7.456677';
const result2 = parseFloat(str1).toFixed(3);
console.log(result2); // 👉️ 5.457
console.log(typeof result2); // 👉️ string

// 👇️ Convert string back to a number
const num2 = 7.79999999;
const result3 = Number(num2.toFixed(3));
console.log(result3); // 👉️ 7.8
console.log(typeof result3); // 👉️ number

In the first example, we used the Number.toFixed method to round a number to 3 decimal places.

The only parameter the method takes is the number of digits that should appear after the decimal point.

In the second example, we have a string that is a valid number.

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const str1 = '7.456677';
const result2 = parseFloat(str1).toFixed(3);
console.log(result2); // 👉️ 5.457
console.log(typeof result2); // 👉️ string

We had to convert it to a number using the parseFloat function because the toFixed method can only be called on numbers.

In the third example, we used the Number object to turn the string that the toFixed method returns into a number.

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const num2 = 7.79999999;
const result3 = Number(num2.toFixed(3));

console.log(result3); // 👉️ 7.8
console.log(typeof result3); // 👉️ number

The number 7.000 is the same as 7, so the trailing zeros get dropped when the value is converted to a number.

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console.log(7.000 === 7); // 👉️ true

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console.log(0.1 + 0.2 === 0.3); // 👉️ false

The sum of 0.1 and 0.2 is equal to 0.30000000000000004 instead of 0.3.

This is because the binary floating-point format cannot accurately represent numbers like 0.1 or 0.2.

The code gets rounded to the nearest number, resulting in a rounding error.

Further Reading #

• Get the number of digits after the Decimal in JavaScript
• Round a Number to 1 Decimal Place in JavaScript