Triangle Perimeter Calculator

What this calculator does

Triangle perimeter is the sum of the three side lengths, but the side lengths must form a valid triangle first.

Simple formulaP = a + b + c.

Validate sidesEach pair of sides must be longer than the third side.

Use casesUseful for fencing, borders, and geometry homework.

For classroom work, check the required rounding rules and whether angles are in degrees or radians. This page uses degrees.

Use Pythagorean theorem or law of cosines depending on the triangle case.

Solve right-triangle side and angle questions with a formula explanation.

Find missing angles from sides or from two known angles.

Solve a triangle when all three sides are known.

Use two sides and the included angle.

Solve common oblique triangle cases.