What this calculator does
This calculator is designed for common triangle homework, geometry, construction, and measurement problems where you know some sides or angles and need the rest.
Three sidesWorks when all side lengths are known.
Semiperimeters = (a + b + c) / 2.
AreaA = √(s(s-a)(s-b)(s-c)).
For classroom work, check the required rounding rules and whether angles are in degrees or radians. This page uses degrees.
Related triangle calculators
More triangle calculators
Find Missing Side
Use Pythagorean theorem or law of cosines depending on the triangle case.
Open calculator →Right Triangle with Steps
Solve right-triangle side and angle questions with a formula explanation.
Open calculator →Triangle Angle Calculator
Find missing angles from sides or from two known angles.
Open calculator →SSS Triangle Calculator
Solve a triangle when all three sides are known.
Open calculator →SAS Triangle Calculator
Use two sides and the included angle.
Open calculator →Law of Cosines
Solve common oblique triangle cases.
Open calculator →