CleanorTools
Factorial

Factorial Calculator

Details

How to use Factorial Calculator

What the tool does, how to run it, and what to expect from the result.

How to calculate a factorial exactly

Enter a whole number and the tool multiplies every integer from 2 up to it, using BigInt arithmetic so that no precision is lost at any size. The result appears immediately and can be copied with one click.

The reason to use an arbitrary-precision tool rather than a calculator app is that factorials outgrow ordinary number types almost immediately. 19 factorial is already beyond exact representation in a double, and 171 factorial is beyond representation at all.

  • Enter a whole number from 0 up to 2,000.
  • Read the result, which is exact to the last digit no matter how long it is.
  • Use Copy result to put the full value on the clipboard rather than trying to select thousands of digits.
  • If you entered a number above 2,000, be aware that it was silently reduced to 2,000.
  • For 0 factorial, expect 1: the empty product is defined as 1.
Tips

Getting a better result out of Factorial Calculator

Specific settings and thresholds, not general advice.

  • The calculation is exact because it uses BigInt. This matters sooner than people expect: 19 factorial already exceeds JavaScript's safe integer limit of 9,007,199,254,740,991, so any calculator using ordinary numbers is giving you wrong digits from 19 factorial onwards.
  • A regular double-precision number overflows to Infinity at 171 factorial. This tool goes on past that without trouble, which is the practical reason to use a BigInt implementation rather than a spreadsheet.
  • The input is capped at 2,000, and the result says when it capped you: type 5,000 and the answer ends with a line telling you it computed 2,000 factorial instead. 2,000 factorial is already 5,736 digits long.
  • 2,000 factorial is a 5,736-digit number. It will fill the result box and it is entirely correct, digit for digit, which is worth remembering before you paste it into anything with a length limit.
  • 0 factorial is 1, and that is a definition rather than a quirk. The empty product is 1 for the same reason the empty sum is 0, and it is what makes the formula for combinations work at the edges.
Limits

What Factorial Calculator does not do

The honest boundary, so you do not lose time finding it yourself.

  • Maximum input of 2,000. The output says when the cap was applied.
  • Whole non-negative integers only. Decimals are floored, and negatives return an instruction rather than a result, so there is no gamma function extension.
  • No permutations, combinations, or double factorial. This computes n factorial and nothing around it.
  • The result is plain text in one box. There is no scientific-notation view and no digit count.
At a glance

Who Factorial Calculator is for

A quick way to understand who this helps, what it solves, and where it connects next.

Best fit

Students, developers, and anyone who needs quick, exact number sequences.

Ideal for

Fast math sequences and number results without a spreadsheet or install.

FAQ

Common questions

Short answers for the questions people usually have before trying a utility like this.

Why do other calculators give me a different answer for large factorials?

Because most of them use floating-point arithmetic, which stops being exact at 19 factorial and overflows entirely at 171 factorial. What you get back looks like a number and is not the right one. This tool uses arbitrary-precision integers, so every digit is correct.

How big can the input be?

2,000. Anything larger is capped, and the output tells you it was capped and what you asked for, so you cannot mistake 2,000 factorial for 5,000 factorial.

Can it do factorials of decimals?

No. The input is floored to a whole number. Factorials of non-integers are defined through the gamma function, which is a different calculation and is not implemented here.

What about negative numbers?

The tool returns a message asking for a whole number of 0 or more. Factorials of negative integers do not exist, because the gamma function has poles there.

How many digits does a large factorial have?

More than most people expect. 100 factorial has 158 digits, 1,000 factorial has 2,568, and 2,000 factorial has 5,736. The tool prints all of them, which is what exact means.

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