Sum of Digits
Calculate the sum of all digits in a number.
Recommended Books on Mathematics
Concrete Mathematics
Ronald L. Graham
Elementary Number Theory
David M. Burton
The Joy of x
Steven Strogatz
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How to Use
Enter a Number
Type any number into the input field.
View the Breakdown
See each digit separated and added together.
Read the Sum
The total sum of all digits is displayed instantly.
Use Cases
Digital Root
"Use the sum of digits as a step toward finding the digital root of a number."
Divisibility Check
"A number is divisible by 3 if its digit sum is divisible by 3."
Math Puzzles
"Solve number puzzles and riddles involving digit sums."
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Frequently Asked Questions
?What is the sum of digits?
It's the total when you add each individual digit of a number. For example, 123 → 1 + 2 + 3 = 6.
?Does it work with large numbers?
Yes. You can enter numbers of any length and get the digit sum instantly.
?What about negative numbers?
The tool ignores the negative sign and sums only the digits.
?How is digit sum used in math?
Digit sums are used in divisibility tests (for 3 and 9), check digits, and digital root calculations.
?What is a digital root?
The digital root is found by repeatedly summing digits until you get a single digit. For example, 99 → 18 → 9.
?Is my data private?
Yes. Everything runs locally in your browser. No data is sent to any server.
?Is this tool free?
Yes. Completely free with no limits, no sign-up required.