Count Digits Calculator

About this calculator

Counting digits sounds trivial but the concept underpins several useful checks: the digit count of a whole number tells you its order of magnitude, the digit sum (adding every individual digit together) is the basis of classic divisibility tests such as “a number is divisible by 3 or 9 if its digit sum is too,” and the count of distinct digits shows how much repetition or variety the number's digits contain.

These properties show up in recreational number theory (digit sums are the building block behind Harshad numbers, digital roots and checksum algorithms like the one used to validate ISBNs and credit card numbers), in programming exercises that practise breaking a number into digits, and in everyday checks like verifying how many digits an ID, account or phone number should have.

Enter any whole number and this calculator reports how many digits it has, what its digits sum to, and how many distinct digit values it uses.