Digit sums underlie divisibility tests (3, 9 and 11), checksums and number puzzles. Seeing the count of each digit also helps when checking long numbers such as IDs or serial numbers.
How to use the Digit Sum Calculator
- Numbers (separate with commas)
- I want to find
- Treatment of numbers
Everything is calculated in your browser, so results appear instantly and nothing you type is sent to a server.
How it works
Choose what to find and whether to treat all numbers as one group or separately. The table lists each digit, how often it appears and its contribution to the total.
Formula
Digit sum = Σ digits; digital root = repeated digit sum; alternating sum = d₀ − d₁ + d₂ − …
Worked example
Inputs — Numbers (separate with commas): 1234, 5678; I want to find: Sum of digits; Treatment of numbers: As a single group.
Results — Result = 36; Digit table = Digit Count Sum
1 1 1
2 1 2
3 1 3
4 1 4
5 1 5
6 1 6
7 1 7
8 1 8
Total 8 36.
Key terms
- Digit sum
- The sum of the digits of a number.
Frequently asked questions
What is the digit sum of 1234?
1 + 2 + 3 + 4 = 10.
How does the digit sum test divisibility?
A number is divisible by 3 (or 9) when its digit sum is.
What is the alternating digit sum for?
Divisibility by 11.
What is the digital root of 1234?
1 (10 → 1).