Triangle Solver: Sides, Angles

Triangle Calculator solves a general triangle. Enter any three known values, including at least one side, and the app works out the missing sides and angles, then the area, perimeter and the lines inside the triangle. It also names the triangle type, for example equilateral acute.

Which three values work

• Three sides

• Two sides and the angle between them

• Two angles and a side

Angles are in degrees, with a degree sign after each field. Leave the unused fields blank: the app needs exactly three filled values.

What the results include

• All three sides and all three angles, in degrees and radians

• Area, perimeter and semiperimeter

• The three altitudes (heights) and the three medians

• Inradius, the radius of the inscribed circle, and circumradius, the radius of the circumscribed circle

Example

Sides 5, 5 and 5 give an equilateral triangle with an area of 10.82532 and a perimeter of 15. The app opens with these values filled in.

Where it helps

• Laying out a triangular garden bed or plot, where you measure two sides and the angle between them

• Checking the angled members of a roof, truss or bracket

• Checking a geometry homework answer step by step

• Working out how much of a triangular panel or sheet a job needs

Good to know

• Two angles together must be less than 180 degrees

• The two shorter sides must add up to more than the longest side

• For right triangles only, the narrower Right Triangle Calculator in More calculators is quicker

Light and dark theme, 28 languages, and a More calculators link to the full Calculator.io app with 170+ tools. Banner ads support the app. Results are for general information.