Triangle Calculator

This calculator finds triangle measurements for construction layouts, schoolwork, and other three-sided problems.

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Enter the available side lengths, base, and perpendicular height requested by the calculator. Use consistent units, and remember that the height must meet the chosen base at a right angle.

Perimeter = side a + side b + side c. Area = base × perpendicular height ÷ 2. For a right triangle, hypotenuse = square root of (leg a² + leg b²).

Worked example

A triangle with a 10-meter base, a 6-meter perpendicular height, and side lengths of 8, 8, and 10 meters has area 10 × 6 ÷ 2 = 30 square meters. Its perimeter is 8 + 8 + 10 = 26 meters.

Common questions

Can three lengths always form a triangle?

No. The sum of any two sides must be greater than the third side. Lengths 2, 3, and 6 fail that test.

Is the slanted side the height?

Usually not. Height is the perpendicular distance from a base to the opposite vertex, even when that line falls outside the triangle.

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