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Excel guide · 3 min read

How to calculate square root in Excel

Quick answerUse =SQRT(B2), where B2 holds the number. You can also raise the number to the power of one half, =B2^(1/2), which also works for other roots such as the cube root =B2^(1/3). SQRT of a negative number returns #NUM!, so check the sign first.

Sample data

Every result on this page was calculated from this sheet by the same spreadsheet engine the Cellwise app uses.

ABCDE
1RoomArea (sq ft)TV width (in)TV height (in)
2Bedroom1444827
3Office110.25
4Patio200
5Garage484
6Sensor test-36

Download this sheet as an Excel practice file (.xlsx)

Method 1: the SQRT function

SQRT takes one number or one cell and returns its positive square root. Here the area of each square room gives the length of one wall. Fill the formula down to do the whole column.

Results are often long decimals: =SQRT(B4) gives 14.142135624 for the patio. Use =ROUND(SQRT(B4),2) to store 14.14.

=SQRT(B2)

Result: 12

12: a 144 sq ft square bedroom is 12 feet on each side.

Method 2: the ^ operator (and the bracket trap)

A square root is the same as raising to the power 1/2, so =B2^(1/2), =B2^0.5 and =POWER(B2,1/2) all return 12. This is the method to use when you need other roots.

The brackets are not optional. Excel does ^ before /, so =B2^1/2 means (B2^1)/2, which halves the number instead.

=16^1/2

Result: 8

8, not 4: Excel calculated 16 to the power 1, then divided by 2. Write =16^(1/2) to get 4.

Negative numbers give #NUM!

Real numbers have no square root below zero, so SQRT(-36) returns #NUM!. Usually that means bad data, like the sensor test row here, so the right fix is to flag it, not to hide it.

=SQRT(B6)

Result: #NUM!

#NUM!, because -36 has no real square root.

Fix: check the sign, or use ABS

Flag negative inputs with IF so the problem is visible. If the sign only shows a direction (for example a loss shown as negative) and you need the root of the size, use =SQRT(ABS(B6)), which gives 6.

To show a negative root, put the minus outside: =-SQRT(B2). Writing =-B2^0.5 fails, because Excel applies the minus sign before the power and tries the root of -144.

=IF(B6<0,"Check value",SQRT(B6))

Result: Check value

Check value, a readable flag instead of #NUM!.

Cube roots and other roots

For the nth root, raise to the power 1/n. A cube root uses 1/3, a fourth root 1/4. POWER(B2,1/3) is the same thing written as a function. Excel has no CBRT function, so ^ or POWER is the way.

=125^(1/3)

Result: 5

5, because 5 x 5 x 5 = 125.

Real use: the diagonal of a screen

Pythagoras gives the diagonal from the width and height: square both, add them, take the root. The same pattern finds distance between two points, and standard deviation is a square root of an average squared difference.

To show the root symbol as text in a label, use Insert > Symbol and pick √ (character code 221A, in the Mathematical Operators subset).

=SQRT(D2^2+E2^2)

Result: 55.072679252

55.07 inches: a 48 x 27 inch screen is sold as a 55-inch TV.

Common mistakes

Writing =B2^1/2

That halves B2. Use brackets: =B2^(1/2).

Writing =-B2^0.5 for a negative root

Excel applies the minus first, so it takes the root of a negative number and returns #NUM!. Use =-SQRT(B2).

Hiding #NUM! with IFERROR

A negative input usually means a data error. Flag it with IF(B2<0,...) so someone checks it.

Expecting both roots

Both 12 and -12 squared give 144, but SQRT only returns the positive root. If your math needs the negative one too (solving a quadratic, for example), add a second cell with =-SQRT(B2).

FAQ

What is the formula for square root in Excel?

=SQRT(number), for example =SQRT(A2). You can also use =A2^(1/2) or =POWER(A2,0.5).

Why does SQRT return #NUM! in Excel?

The number is negative. Check the input, or use =SQRT(ABS(A2)) if you need the root of the size only.

How do I calculate a cube root in Excel?

Raise the number to the power 1/3: =A2^(1/3) or =POWER(A2,1/3). There is no separate cube root function.

How do I take the square root of a whole column?

Write =SQRT(B2) next to the first value and double-click the fill handle to copy it down. In Excel 365 you can also write =SQRT(B2:B5) once and the results spill down by themselves.

How do I square a number in Excel?

Use =A2^2 or =POWER(A2,2). SQRT undoes it: =SQRT(A2^2) gives back A2 for positive numbers.

Functions used

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