Q&A for How to Find a Square Root Without a Calculator

There are two ways to do it: (1) If you can measure the inside diagonals (from a corner to its opposite corner), the diagonals of a perfect rectangle are equal to each other; (2) Get a magnetic compass and sight it along two adjacent sides. The two directions should be exactly 90° from each other.

Use a factor tree. For example, 625 = 5 x 125 = 5 x 5 x 25 = 5 x 5 x 5 x 5. Because there are 4 fives, and we are looking for the square root, (5 x 5)(5 x 5) = 625. Therefore the square root of 625 is 25.

The number 1089 is the answer. The way you work it out is 1008 is a 9 time table number. Then just add on nines starting at this number, and the first 9 times table number you get that has two even digits and odd digits is your answer.

Use the Pythagorean theorem to find the third side, then add the sides together.

To rationalize a denominator, multiply the fraction by a "clever" form of 1. In other words, you need a fraction whose numerator and denominator are both equal to the square root in the denominator.

There's only one step: multiply the number by itself. x² = (x)(x).

Since the square root of 24 is not an integer, you'll have to accept a decimal.

See Calculate a Square Root by Hand .

There is no such formula. See Calculate a Square Root by Hand .

For cubed roots, the cubed root multiplied by itself 3 times will give you the number. So, mathematically, if the quotient obtained on dividing a number by any number is the square of the second number, that's your cubed root. For example, 216/6=36, which is the square of 6. Thus, 6 is the cube root of 216.

There's no shortcut, assuming you're not using a log table. Manually multiply the number by itself.

Unfortunately, no. The technique shown above is one way to do it without using a calculator, logarithm tables or a slide rule. There are other techniques, too, that consist of a series of successively closer estimations.

Assuming you're not using a calculator, you could square 200 (that's 40,000), and to that add the square of 8 (which is 64). 40,000 + 64 = 40,064.

That means that n is the square root of 9, which is 3.

Not that anyone's been able to discover.

If you're not allowed to multiply (or use a calculator), you would have to add up 21 21's by hand.

Not in any practical sense. You could use division in a process of trial-and-error, but it could prove to be quite cumbersome in many cases. (In a case where the number happened to be a perfect square, the trial-and-error process could be relatively quick and easy.

40.

The square root of 2 is 1.414. 10 times that is 14.14.