Digit sum and digital root calculator
Paste a long number to get the sum of its digits and its digital root, the single digit left after repeated summing. Handy for quick arithmetic checks and divisibility rules.
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Processing and privacy: The result is calculated inside your browser and your data is not sent to any server.
How to use it
- Enter number.
- The result appears straight away and updates as you edit.
- Copy the result, or copy a link that keeps the same values to share it.
How it is calculated
Digit sum = the sum of every digit. Digital root = 0 for 0, otherwise 1 + ((digit sum - 1) mod 9).
Example
Inputs: Number = 987654321. Result: Digit sum: 45; Digital root: 9; Number of digits: 9.
Limits and caveats
- Accepts whole numbers up to 100000 digits and ignores signs, commas and spaces.
- Decimal fractions are not accepted.
Questions about this tool
What is a digital root?
The single digit you reach by summing digits again and again. For 12345: 15, then 1 + 5 = 6.
How does the digit sum help with divisibility?
A number is divisible by 3 exactly when its digit sum is, and the same rule works for 9.
Can I type Arabic-Indic digits?
Yes, digits like ٤٥٦ are read as 456 automatically.