Right triangle (Pythagoras)
Hypotenuse, legs and angles of a right triangle; check square corners with the 3-4-5 rule.
Tool
Tools › Geometry and measurement
How it is calculated
Pythagorean theorem: hypotenuse² = a² + b². If you know the hypotenuse h and one leg a: b = √(h² − a²).
3-4-5 rule to set out a right angle on site: mark 3 m on one side and 4 m on the other; the corner is square when the diagonal measures exactly 5 m. Any multiple works (6-8-10, 0.9-1.2-1.5).
Keep in mind
- When setting out a house, also check that both diagonals of the rectangle are equal.
- Other useful whole-number triples: 5-12-13 and 8-15-17.