JavaScript Math.random() explain the difference between Math.ceil() vs Math.floor() vs Math.round()

In JavaScript to generate a random number we use Math.random() and it returns numbers between 0 and 1.

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console.log(Math.random()); // 0.587777376294869

console.log(Math.random()); // 0.2197126264732836

console.log(Math.random()); // 0.9785932144070053

If we want to get a random number between 0 and 10 we just need to multiply the result of Math.random() by 10 and round the result.

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console.log(Math.random() * 10); // 9.357923991790457

console.log(Math.random() * 10); // 3.5154493888867466

console.log(Math.random() * 10); // 5.1469888802577035

Still, as we can see the numbers are floating-point and usually we want to have integers. The solution is pretty simple and now with help comes 3 methods how we can achieve it:

• Math.round()
• Math.floor()
• Math.ceil()

Math.round() - round to the nearest number (integer e.g. 1,5,10)
e.g.:

• 1.23 will be rounded to 1
• 5.92 will be rounded to 6

Example how to generate a random number between 0 and 10 with Math.round().

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console.log(Math.round(1.23)); // 1

console.log(Math.round(5.92)); // 6

​

console.log(Math.round(Math.random() * 10)); // 2

console.log(Math.round(Math.random() * 10)); // 9

console.log(Math.round(Math.random() * 10)); // 5

Math.floor() - round DOWN to the nearest number
e.g.:

• 1.23 will be rounded to 1
• 5.92 will be rounded to 5

Example how to generate random numbers between 0 and 10 with Math.floor().

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console.log(Math.floor(1.23)); // 1

console.log(Math.floor(5.92)); // 5

​

console.log(Math.floor(Math.random() * 10)); // 3

console.log(Math.floor(Math.random() * 10)); // 1

console.log(Math.floor(Math.random() * 10)); // 6

Math.ceil() - round UP to the nearest number
e.g.:

• 1.23 will be rounded to 2
• 5.92 will be rounded to 6

Example how to generate random numbers between 0 and 10 with Math.ceil().

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console.log(Math.ceil(1.23)); // 2

console.log(Math.ceil(5.92)); // 6

​

console.log(Math.ceil(Math.random() * 10)); // 5

console.log(Math.ceil(Math.random() * 10)); // 7

console.log(Math.ceil(Math.random() * 10)); // 3

1. Math.random method - Mozilla Docs
2. Math.round method - Mozilla Docs
3. Math.floor method - Mozilla Docs
4. Math.ceil method - Mozilla Docs