Find the right triangle tool
Triangle Solver with Steps
Use this triangle solver with steps to calculate missing sides, angles, area, and perimeter for common triangle cases.
Open calculator →Find Missing Side of Triangle Calculator
Find a missing triangle side using the Pythagorean theorem for right triangles or the law of cosines for SAS cases.
Open calculator →Right Triangle Calculator with Steps
Solve a right triangle from any two sides. Find the hypotenuse, missing leg, angles, area, and perimeter with steps.
Open calculator →Triangle Angle Calculator
Calculate triangle angles from three sides or find the third angle when two angles are known.
Open calculator →Triangle Area Calculator
Calculate triangle area from base and height or from three side lengths using Heron’s formula.
Open calculator →Triangle Perimeter Calculator
Calculate the perimeter of a triangle from three side lengths and check whether the side lengths form a valid triangle.
Open calculator →Triangle Height Calculator
Find triangle height from area and base, or calculate altitudes from three sides using Heron’s formula.
Open calculator →Isosceles Triangle Calculator
Calculate height, area, perimeter, base angles, and vertex angle for an isosceles triangle.
Open calculator →Scalene Triangle Calculator
Solve a scalene triangle from three unequal side lengths and calculate angles, area, and perimeter.
Open calculator →Equilateral Triangle Calculator
Calculate area, height, perimeter, and angles for an equilateral triangle from one side length.
Open calculator →Acute Triangle Calculator
Calculate the angles of a triangle from three sides and check whether all angles are acute.
Open calculator →Obtuse Triangle Calculator
Calculate triangle angles from three sides and check whether the triangle is obtuse.
Open calculator →SSS Triangle Calculator
Solve a triangle from three side lengths using the law of cosines and Heron’s formula.
Open calculator →SAS Triangle Calculator
Solve a triangle from two sides and the included angle using the law of cosines.
Open calculator →ASA Triangle Calculator
Solve a triangle from two angles and a known side using the angle sum rule and law of sines.
Open calculator →AAS Triangle Calculator
Solve a triangle from two angles and a non-included side using the law of sines.
Open calculator →SSA Triangle Calculator
Solve the SSA triangle case and check whether there is one solution, two solutions, or no valid triangle.
Open calculator →Law of Cosines Triangle Calculator
Use the law of cosines to find a missing side from two sides and an included angle, or to find angles from three sides.
Open calculator →Law of Sines Triangle Calculator
Use the law of sines to solve triangles when you know angles and at least one side.
Open calculator →Heron’s Formula Calculator
Calculate triangle area from three side lengths using Heron’s formula, plus perimeter and semiperimeter.
Open calculator →When to use each formula
| Known information | Best page | Typical formula |
|---|---|---|
| Three sides | SSS Triangle Calculator | Law of Cosines + Heron’s formula |
| Two sides and included angle | SAS / Law of Cosines | c² = a² + b² − 2ab cos(C) |
| Two angles and one side | ASA / AAS / Law of Sines | a/sin(A) = b/sin(B) = c/sin(C) |
| Right triangle with two sides | Right Triangle Calculator | a² + b² = c² |
| Three sides and area needed | Heron’s Formula Calculator | A = √(s(s-a)(s-b)(s-c)) |
Start from the information you already have
Triangle problems are easier when you choose the calculator by known values rather than by the final answer. If your question says “find the missing side,” first decide whether the triangle is right-angled, SAS, or a law of sines case.
Popular triangle questions
| Question | Recommended page |
|---|---|
| How do I find the missing side of a triangle? | Find Missing Side of Triangle Calculator |
| How do I solve a right triangle with steps? | Right Triangle Calculator with Steps |
| How do I find triangle angles from three sides? | Triangle Angle Calculator |
| When should I use the law of cosines? | Law of Cosines Triangle Calculator |
| When should I use the law of sines? | Law of Sines Triangle Calculator |