Either of the two sides of a right triangle that is not the hypotenuse.
In math, legs are the two sides that form the right angle.
A right triangle is a triangle with one right angle (a 90° angle). The two legs form this right angle, and the longest side across from it is called the hypotenuse.
You can think of the legs like the base and height of the triangle; they meet at the corner that forms the 90° angle.
We often use the legs when working with:
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The Pythagorean Theorem: a² + b² = c², where a and b are the legs and c is the hypotenuse.
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Finding the area of a triangle: In a right triangle, the legs serve as the base and height, used in the formula Area = \(\Large\frac{1}{2}\) (base × height).
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Solving problems in geometry and trigonometry: Using relationships between sides to find missing angles or distances.
When Do Students Learn About Triangle Legs?
Students first learn about triangle parts, including legs, when studying right triangles in upper elementary or middle school.
Grades 5–6 – Introduction to Right Triangles
Students begin identifying triangle types, including right triangles, and naming triangle sides such as legs and hypotenuse.
Grades 7+ – Using Triangle Legs in Geometry
Students use triangle legs in formulas such as area and the Pythagorean Theorem, and later apply them in geometric reasoning. In higher grades, triangle legs are used in trigonometric ratios.
