Excel SQRT Function — How to Use It (with 3 Examples)

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What does SQRT do?

SQRT returns the square root of a number. It only works with positive numbers (or zero) — negative inputs return a #NUM! error.

In real spreadsheets it shows up most often inside statistical formulas, like calculating standard deviation manually or working out margin of error.

=SQRT(number)

Argument	Description
number required	The number to find the square root of. Must be zero or positive.

Example 1

Basic square root

=SQRT(81)

Returns 9.

Example 2

Square root of a negative becomes an error

=SQRT(-9)

Returns #NUM! — wrap in ABS first if you specifically need the root of a negative magnitude: =SQRT(ABS(-9)).

Example 3

Margin of error calculation

=1.96*(STDEV/SQRT(n))

A simplified margin-of-error formula — error shrinks with the square root of sample size, not proportionally to it.

⚠️ Feeding SQRT a negative number directly

This always errors. If you mean the magnitude, wrap the input in ABS first.

Does SQRT work with decimals?

Yes — =SQRT(2) returns approximately 1.414.

Practice this formula yourself — type it in a real spreadsheet and get instant feedback. Free, no download needed.

POWER ABS STDEV