Right Triangle Calculator

Pythagorean theorem: a^2 + b^2 = c^2, so c is the square root of (a^2 + b^2), and a leg is the square root of (c^2 minus the other leg squared). Angle A = arctan(a / b) in degrees, and angle B is 90 less that. Area is half of a x b.

How do I check that a corner is square?

Measure 3 ft along one side and 4 ft along the other. If the diagonal between those marks is exactly 5 ft, the corner is square. On a large deck use 6, 8 and 10 for more accuracy, which is the same triangle doubled.

What is the hypotenuse?

The longest side, always the one opposite the right angle. It is the only side the theorem solves for by adding rather than subtracting, which is a useful way to remember which case you are in.

Does this work on any triangle?

No. The Pythagorean theorem only holds when one angle is exactly 90 degrees. For other triangles you need the law of cosines, which is the general form this is a special case of.