Choose whether you want the hypotenuse or a side, then enter the two known lengths.
Formula
a² + b² = c²
Worked example
Sides of 3 and 4 give a hypotenuse of √(9 + 16) = 5.
Frequently asked questions
When does the theorem apply?
Only in a right triangle, one with a 90° angle.
Which side is the hypotenuse?
The longest side, opposite the right angle.
How do builders use it?
The 3-4-5 rule checks that a corner is square.
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Results are estimates for information only. Check important figures with a professional.