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Factorial Calculator

Factorial Calculator is part of Toolspire and is ready as soon as this page loads. The result is the full integer, not a rounded scientific notation. 5! is 120. Past 500 the page stops so the tab does not build a huge string.

Runs in this tabFreeNo account

On this page

What you can do here

Exact digits

Floating point cannot hold 25! exactly. BigInt keeps every digit.

A published ceiling

500! is allowed. 501 is refused so a pasted accident does not lock the tab.

Digit count beside the integer

You can check a large factorial by its length even when you do not re-multiply every step.

The sequence

How to use the Factorial Calculator

  1. 1

    Type a whole n

    Decimals are rejected. Factorial is not defined for 4.5 on this page; that would be a gamma function.

  2. 2

    Start from a known value

    Try 5 and confirm 120, or 0 and confirm 1, before you trust a large result.

  3. 3

    Copy the full integer

    The headline is the entire factorial. The copy button takes that string, not the digit count.

Worth knowing

  • Factorial Calculator on Toolspire: n! is 1 × 2 × … × n, computed with BigInt so 20! is exact, not a rounded float.
  • 0! is 1 by the empty-product convention. That value is what makes nPr formulas work when r = n.
  • The page accepts integers from 0 to 500. 10! is 3,628,800.
  • The detail line is the digit count of the full integer, which is the useful check once the number no longer fits on one glance.

Why 0! is 1 here

The product of no numbers is defined as 1 so that n! = n × (n−1)! still holds when n is 1. Permutations use that fact: the number of ways to arrange n items out of n is n! / 0! = n!. This calculator follows that convention. It does not compute the gamma function for fractional n, and it does not switch to scientific notation.

FAQ

Questions about Factorial Calculator

Where does Factorial Calculator run?

Factorial Calculator runs in this tab on Toolspire. What you type or drop in is not sent to us and is not stored on a server.

What is 0 factorial?

1. The page returns that on purpose. It is the value used in permutation formulas when you arrange every item.

How far can n go?

500. Above that the page returns no result. The integer would be enormous and slow to build in a tab.

Why is 20! not written with an e?

Because it is exact. A floating-point factorial would round. BigInt keeps the digits.

Is factorial defined for negatives?

Not in this school definition. Negative n is rejected.

Keep going

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