Principal real root
For real-number output, this calculator accepts values of 0 or greater. The principal square root of 144 is 12, even though both 12 and -12 square to 144.
Example
The square root of 81 is 9 because 9 x 9 = 81. For non-perfect squares, the result is a decimal approximation.
Common mistakes
Do not forget that the calculator returns the principal non-negative root. Solving x^2 = 81 has two solutions, 9 and -9, but sqrt(81) is written as 9.
Limitations
Negative values require complex numbers, which are outside this simple real-number calculator.
Last reviewed: 2026-05-17