Factorial Calculator

Factorial Calculator computes n!, the product of every whole number from one up to n, and writes the multiplication out for small values so the definition is visible rather than assumed. Ten factorial is 3,628,800, which is the number of different orders ten things can be arranged in.

Factorials grow faster than any exponential function, and seeing it is the point of the digit count. Ten factorial has seven digits; twenty factorial has nineteen; a hundred factorial has a hundred and fifty-eight. That growth is why so many counting problems become intractable quickly, and why 170 is the last factorial a double-precision number can hold.

Zero factorial is one, which looks like a trick and is not. There is exactly one way to arrange an empty collection, and defining it as one is what makes the formulas for permutations and combinations work at their boundaries. Both of those counts are shown here when you give an r value.

The page shows its working, not just its answer. Where there is a formula it is printed with your own numbers substituted in, so you can check the result rather than take it on trust -- which is the difference between a calculator you can use for something that matters and one you cannot.

Everything runs inside your browser. What you type is never uploaded, never logged and never stored, and the calculator keeps working if your connection drops after the page has loaded.

• Shows n!, digits, permutations npr, combinations ncr and n! / (n-1)! together, so you are not running it twice
• Prints the formula with your own figures substituted in
• Updates as you type, with no button to press and no page reload
• Copy the result in one click
• Free, no sign-up, and it runs entirely in your browser

The factorial calculator is used by writers, developers, students, marketers and anyone else who needs the job done once without installing software. Common cases include:

• Counting the arrangements of a set of items
• Working out a permutation or combination by hand
• Checking a probability calculation that uses factorials
• Seeing how quickly factorial growth outruns exponential growth