How this calculator works
A square is a rectangle whose four sides are equal, so one measurement settles everything: the area is the side squared, the perimeter is four sides, and the diagonal is the side times the square root of 2. Negative sides are rejected; zero gives a degenerate square.
Formula
Area = s²; Perimeter = 4s; Diagonal = s√2.
Worked example
A side of 7 gives area 49, perimeter 28 and diagonal 7√2 ≈ 9.8995. A side of 2.3 gives area 5.29, perimeter 9.2 and diagonal ≈ 3.2527.
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Frequently asked questions
Why keep a separate square calculator?
One input answers the three most common square questions directly; the rectangle calculator gives the same numbers when you enter equal sides.
What is the diagonal exactly?
It is the side multiplied by √2, an irrational number approximately equal to 1.41421, from the Pythagorean theorem on two equal sides.