How to Calculate Standard Deviation in Excel

Excel has two main standard deviation functions:

• STDEV.S Sample standard deviation. Use this when your data is a sample of a larger group.
• STDEV.P Population standard deviation. Use this when your data represents the entire group.

In most everyday cases, STDEV.S is the right pick. If you are not sure which one matches your situation, default to STDEV.S.

Older workbooks may also use STDEV and STDEVP. Microsoft kept them for backwards compatibility, but recommends the .S and .P versions in modern Excel because the names make the sample-vs-population choice explicit.

Both functions compute the same kind of spread around the mean. The difference is in the denominator:

• STDEV.S divides by n − 1 (the count minus one). This is Bessel's correction.
• STDEV.P divides by n (the total count).

If you have measurements for an entire group (every employee in a small company, every test score in one class), STDEV.P is correct. If your numbers are a sample of a bigger group (a survey of 100 customers, 30 days of stock prices), STDEV.S is correct.

For the underlying formulas in detail and a step-by-step walkthrough of the math, see Standard Deviation Formula. For a deeper look at the underlying choice between sample and population, which is what STDEV.S and STDEV.P really are, see Sample vs Population Standard Deviation.

Use STDEV.S. The syntax is:

You can pass:

• A range of cells: =STDEV.S(A2:A9)
• A list of values: =STDEV.S(2, 4, 4, 4, 5, 5, 7, 9)

Excel returns the sample standard deviation. Blank cells and text values inside the range are ignored automatically.

Use STDEV.P. Same syntax, just swap the function name:

Or with a list of values:

The result is the population standard deviation, with the same handling of blanks and text.

We will use the same small data set used across the other standard deviation guides:

The next four sections walk through the calculation in Excel one step at a time.

Open Excel and put each number in its own cell, top to bottom in a single column.

• A1: a header label like “Score” (optional but useful for clarity)
• A2 through A9: the eight values, one per cell

Avoid putting totals or summary rows inside the data range. They will skew the result if Excel treats them as data points.

Decide which formula matches your data. For this example, treat the eight values as a sample, so reach for STDEV.S. If those eight values were the entire population (every score in a small class, for instance), you would use STDEV.P instead.

This decision matters: the two functions give different answers on the same data, especially with small data sets.

In an empty cell (say B2), type:

Press Enter. Excel returns approximately 2.138.

For the population version, use =STDEV.P(A2:A9), which returns exactly 2.

Excel's number is fast, but it is worth a sanity check the first time you use a new formula. Two ways to check:

1. Open the standard deviation calculator, paste the same numbers, and compare. The calculator reports both sample and population standard deviation alongside the mean and variance, so the figure you want should match exactly.
2. For a small data set, doing the manual math once is the most thorough check. See Standard Deviation Formula for the step-by-step walkthrough.

If your Excel result and your check disagree, the most common culprit is using the wrong function (sample vs population).

A few traps that catch people:

• Mixing up STDEV.S and STDEV.P. Easy to do, big difference in result, especially with small data sets.
• Numbers stored as text. STDEV.S and STDEV.P automatically ignore text values, so if a cell contains a number stored as text, that value is silently excluded. Look for tiny green triangles in the corner of cells, which Excel uses to flag this.
• Including totals or headers in the range. =STDEV.S(A1:A10) where A1 is “Score” and A10 is a sum row will give a misleading answer.
• Using the legacy STDEV function. It is identical to STDEV.S in modern Excel, but using STDEV.S makes your sample-vs-population intent clear to anyone reading the workbook later.
• Forgetting to fix references. If you copy the formula across columns, =STDEV.S(A2:A9) becomes =STDEV.S(B2:B9), which may or may not be what you wanted.

Variance has its own pair of Excel functions (VAR.S and VAR.P) that work the same way. For the relationship between variance and standard deviation, see Variance vs Standard Deviation.

Both Excel and a dedicated calculator use the same underlying math. The choice is about context.

• Use Excel when your data already lives in a spreadsheet and you want the result inline with other analysis.
• Use the standard deviation calculator when you want a quick answer outside Excel, when you do not have Excel handy, or when you want to double-check an Excel result.

For a longer plain-language explanation of what the result actually means, see What Is Standard Deviation?

• STDEV.S is sample standard deviation. Use this most of the time.
• STDEV.P is population standard deviation. Use only when you have data for the whole group.
• Syntax: =STDEV.S(range) or =STDEV.S(value1, value2, ...).
• Excel ignores blank cells and text inside the range automatically.
• Watch for numbers stored as text, headers, and totals leaking into the range.
• Cross-check with the standard deviation calculator if a result looks off.