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About this tool
Exact factorial (n!) of a whole number using big integers.
The Factorial Calculator computes n! — the product of every whole number from 1 to n — exactly, for any n from 0 to 2000, using arbitrary-precision big integers rather than floating-point arithmetic. That matters because a standard 64-bit double stops representing factorials exactly at 23!, while this returns every digit: 100! comes back as its full 158-digit value, and 2000! as all 5,736 digits. Alongside the number you get its digit count, so you can see the scale at a glance.
Open Factorial Calculator on AltFTool — it loads instantly in your browser.
Type a value into the 'n (0–2000)' field, which starts at 20; the calculator rounds decimals down before checking the range, while a resulting value below 0 or above 2000 shows a dash and 'Enter a whole number 0–2000'.
There is no Calculate button — the Result updates as you type, printing 'n! =' followed by the value, cut to its first 30 digits with an ellipsis when it is longer, and a caption counting the total digits.
Read the complete exact factorial from the 'Full value' card below the result, or use Copy or Download to save the whole number as factorial-calculator.txt.
Every digit is computed with big-integer multiplication, so results past 23! are correct instead of rounded to the nearest representable double.
The output reports how many digits the answer has, which is often the number you actually wanted when comparing magnitudes.
The headline shows a truncated preview so the layout stays readable, while the complete integer is listed in full underneath.
0! = 1. It is the empty product — multiplying no numbers together gives the multiplicative identity — and defining it this way keeps formulas such as nCr = n! / (r!(n-r)!) correct when r equals 0 or n.
2000, which produces a 5,736-digit result. The input must be a whole number from 0 to 2000; negative values are rejected, and decimals are floored to a whole number, because the plain factorial is only defined on non-negative integers.
Because they use floating-point numbers, which keep roughly 15-17 significant digits and switch to scientific notation beyond that. Factorials stop being exactly representable as a 64-bit double from 23! onward, so this tool uses big integers and returns all 158 digits of 100! instead.
Not here — the input is floored to a whole number. Non-integer factorials are defined through the gamma function, where n! = Γ(n+1), so 4.5! is Γ(5.5), roughly 52.34; that needs a gamma-function calculator rather than a product of integers.
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