What is it?
The Triangle Calculator solves a triangle from the sides and angles you know. It finds the missing sides and angles, the area, the perimeter and the type of triangle.
Who is it for?
Students of trigonometry, surveyors, builders and anyone solving triangles from sides and angles.
How to use it
Choose what I know: Three sides, Two sides and the angle between, or Two angles and the side between. Fill in the values (angles in degrees). The answer appears as you type; there is no Calculate button. Tap Copy result to copy it, or Share on WhatsApp to send it.
Labelling
Each angle sits opposite the side with the same letter: angle A is opposite side a. Angle C (between a and b) is where sides a and b meet.
No answer?
- Three sides: the two shorter sides together must be longer than the longest. 3, 4 and 8 can’t make a triangle.
- Angles must add up to less than 180°.
Uses
Land plots and roofs, surveying, navigation and trigonometry homework. For right triangles, the Pythagoras Calculator is simpler. The Area Calculator handles four-sided plots.
It uses the law of cosines and the law of sines.
Errors and how to fix them
- “These sides cannot make a triangle”
- “The angle must be between 0 and 180”
- “The two angles must add up to less than 180”
Open the tool: Triangle Calculator
Still stuck?
Contact support. Tell us which tool or page you were using, what you tapped, what you saw, and your phone or computer and browser (for example: Android phone, Chrome). We reply by email.
Questions, or an error not listed here?
Tell us in the comments: what you were doing, the exact message you saw, and your device and browser. We read every comment and add new fixes to this article.