Factorial Calculator (n!)
Enter any non-negative whole number and calculate its factorial instantly. This tool computes exact values using big integer math.
If you are trying to figure out how to do factorial on a calculator, you are in the right place. Whether you are using a scientific calculator, a graphing calculator, or just your phone, factorial is one of the most useful functions in math, statistics, and probability.
How to do factorial on a scientific calculator
Method 1: Use the dedicated x! key
Most scientific calculators include a factorial key labeled x!. On many models, it is accessed directly or via a shifted function (like SHIFT or 2nd).
- Type a non-negative integer (for example, 7).
- Press the x! key (or SHIFT + key where x! is printed).
- Press =.
- You should get 5040 for 7!.
Method 2: Graphing calculators (TI, Casio, HP)
On graphing calculators, factorial is usually in a math/probability menu:
- TI calculators: MATH → PRB → !
- Casio models: OPTN/PROB menus or SHIFT combinations
- HP models: often found in combinatorics or special functions
What is factorial? (Quick refresher)
The factorial of a number n, written n!, is the product of all positive integers from 1 to n.
- 0! = 1
- 1! = 1
- 2! = 2
- 3! = 6
- 5! = 120
- 10! = 3,628,800
So, if your teacher asks you for 6!, you compute: 6 × 5 × 4 × 3 × 2 × 1 = 720.
Why factorial matters in real math problems
Factorials appear constantly in combinatorics and probability. Anytime you are counting arrangements or combinations, factorial is probably involved.
- Permutations: number of ways to arrange items
- Combinations: number of ways to choose groups
- Binomial coefficients: nCr and Pascal’s triangle
- Series and calculus: Taylor/Maclaurin expansions
Common errors when using factorial on calculator
1) Decimal input
Most standard calculators only define factorial for whole numbers. If you enter 4.5! on a basic scientific model, you may get an error.
2) Negative input
Factorial for negative integers is undefined in basic arithmetic. Entering -3! often causes domain errors.
3) Number too large
Even if the operation is valid, your device may overflow. Factorials grow extremely fast. For instance, 20! is already over 2 quintillion.
4) Wrong menu/key sequence
On many calculators, factorial is hidden behind SHIFT/2nd functions. If nothing happens, check the key legend and mode.
No factorial button? Do it manually
If your calculator has no x! key, multiply descending integers:
- For 8!, compute 8 × 7 × 6 × 5 × 4 × 3 × 2 × 1
- Use memory keys to avoid mistakes on long products
- For bigger numbers, use an online factorial calculator (like the one above)
FAQ: factorial on calculator
Can I do factorial on my phone calculator?
Some phone calculators include scientific mode with x!. Rotate to landscape or enable advanced mode. If unavailable, use a web calculator.
What is the largest factorial my calculator can handle?
It depends on the model. Many handheld calculators overflow around 69! to 170! for floating-point display, while software calculators can go much higher.
Is 0! really equal to 1?
Yes. By definition in combinatorics and algebra, 0! = 1. This keeps formulas consistent (especially combinations and series).
Can factorial be used with combinations (nCr)?
Absolutely. The combinations formula is nCr = n! / (r!(n-r)!), so factorial is the foundation of many counting problems.
Final takeaway
If you need to compute factorial quickly, use the x! key on your scientific calculator or the calculator on this page. Keep inputs as non-negative integers, and remember that results get huge very quickly. Mastering factorial now will make probability, algebra, and statistics much easier later.