Digit sum calculator
Add all the digits of any number. Also computes the digital root — the single-digit result of repeated summing.
Number
What is digit sum?
The digit sum is the total of all individual digits. For 12345: 1+2+3+4+5 = 15.
Digital root
Keep summing digits until you get a single digit. 12345 → 15 → 6. The digital root of 12345 is 6.
Divisibility tests
A number is divisible by 3 if its digit sum is divisible by 3. A number is divisible by 9 if its digit sum is divisible by 9. For 12345: digit sum = 15, which is divisible by 3 but not 9.
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