Standard deviation calculator
Calculate sample and population standard deviation.
The standard deviation calculator takes a pasted list of numbers and computes the count, mean, and both sample (dividing by n−1) and population (dividing by n) standard deviation — showing both since which one applies depends on whether your data is a sample or the entire population.
How to use
- Paste a list of numbers, one per line or comma-separated.
- See the count, mean, and both the sample (n−1) and population (n) standard deviation.
Common use scenarios
- Measuring how spread out a set of values is.
- Getting the sample standard deviation needed for a statistical test.
- Checking a data set's spread before using it as input to another calculator (like a T-score or Z-score).
- Double-checking a spreadsheet's STDEV or STDEVP formula result.
✓Content & verification reviewed: 2026-08-25
How we verify Standard deviation calculator
How to confirm you're reading the right one of the two SD values.
Sample SD (n−1) vs. population SD (n) — pick based on what your data represents
Use the sample standard deviation if your numbers are a sample drawn from a larger population (the common case in most statistical tests); use the population standard deviation only if your numbers are the entire population you care about — this choice usually matters more than people expect, especially with a small count.
Non-numeric entries are silently ignored
Any line or comma-separated entry that isn't a valid number is dropped from the calculation without a separate warning — if your count looks lower than the number of lines you pasted, check for stray text, blank lines, or typos in your input.
At least 2 valid numbers are required
Standard deviation is undefined for a single value, so if fewer than 2 valid numbers remain after non-numeric entries are dropped, no result is shown at all rather than a misleading zero.
Before you rely on the result
- You've decided whether your data is a sample (use n−1) or the full population (use n) before reading the result.
- The count shown matches the number of valid numbers you expected — check for silently dropped non-numeric entries if not.
- You've pasted at least 2 valid numbers, since a result won't show otherwise.
- If comparing against a spreadsheet, you've matched STDEV/STDEV.S to the sample value and STDEVP/STDEV.P to the population value.
Who this is for
- Anyone measuring how spread out a set of values is.
- People needing sample standard deviation for a statistical test.
- Anyone checking a data set's spread before further calculations.
- People double-checking a spreadsheet's STDEV or STDEVP result.
Real-world examples
Preparing input for a statistical test
Someone running a t-test by hand needs the sample standard deviation of their data, pastes the values here, and reads off the sample SD to plug into the test formula.
Comparing spread across two groups
A researcher comparing the variability of two data sets computes the standard deviation for each and compares which group's values are more tightly clustered around its mean.
Verifying a spreadsheet formula
Someone who computed STDEV in a spreadsheet pastes the same numbers here to confirm the sample standard deviation matches, catching any accidental range-selection error in the spreadsheet.
Limitations
- Non-numeric entries are ignored; if fewer than 2 valid numbers remain, no result is shown.
Frequently asked questions
Should I use the sample or population standard deviation?
Use the sample SD (n−1) if your numbers are a sample from a larger population — this is the more common case. Use the population SD (n) only if your numbers represent the entire population you're studying, with nothing left out.
Why is my count lower than the number of lines I pasted?
Non-numeric entries — stray text, blank lines, or typos — are silently dropped from the calculation, which lowers the count without a separate warning. Check your input for anything that isn't a valid number.
What if I only have 1 number?
No result is shown — standard deviation requires at least 2 valid numbers, since it's a measure of spread that's undefined for a single value.
How do I match this against my spreadsheet's formulas?
This tool's "sample standard deviation" corresponds to STDEV or STDEV.S in most spreadsheets, and "population standard deviation" corresponds to STDEVP or STDEV.P.
🔒 Runs in your browser — nothing is uploaded. Results are for reference only; see the disclaimer. Last updated: 2026-08-25
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