Result
Square Root Calculator
Find the principal square root of a non-negative number.
Frequently asked questions
Is this square root calculator free?
Yes. It is completely free, works in your browser and does not require an account.
Does it work on mobile?
Yes. EasyToolsCalc is responsive and works on phones, tablets and desktop computers.
Are my values saved?
No. The calculation runs locally in your browser. EasyToolsCalc does not save the numbers you enter.
Find the principal real square root
Method and inputs
Enter a non-negative number. The calculator returns the principal square root, the non-negative value that squares to the input. For a perfect square the result is an integer; other roots are generally approximated. The display rounds to five decimal places.
Worked example
The square root of 81 is 9 because 9 × 9 = 81. The square root of 2 is approximately 1.41421; squaring that rounded value gives an approximation rather than exactly 2. For a square with area 49 square metres, the side length is 7 metres.
Limits and common mistakes
The equation x² = 81 has two solutions, +9 and −9, but the principal square root √81 means +9. Negative inputs have no real square root and are rejected by this real-number calculator. Zero has square root zero. The square root of a sum is generally not the sum of the roots: √(9 + 16) = 5, while √9 + √16 = 7.
Can I recover the original value by squaring the display?
Only approximately when the root is rounded. Keep full precision for later calculations when accuracy matters. If the input has units of area, its square root has units of length; this does not mean any rectangular area determines a unique side length.
Content updated: 2026-10-03.