Toolstia / Triangle calculator
Triangle calculator
Give the triangle calculator three known values and it works out everything else: all three sides, all three angles, the area, the perimeter, the three heights, and the radii of the inscribed and circumscribed circles. It also names the triangle type.
Side a is opposite angle A, side b opposite B and side c opposite C.
How it works
- Choose what you know: SSS, SAS or ASA.
- Enter the three values.
- Read the solved triangle.
Laws used
The law of cosines handles SSS and SAS. The law of sines handles ASA. Angles always add up to 180°.
Triangle type
The tool says whether the triangle is equilateral, isosceles or scalene, and whether it is acute, right or obtuse.
Invalid triangles
Three sides only make a triangle if each is shorter than the other two added together, and the angles in ASA must add up to less than 180°.
Extra results
Area comes from Heron’s formula. The inradius is area ÷ half the perimeter and the circumradius is abc ÷ 4 × area.
Questions
Why not SSA?
Two sides and a non-included angle can give zero, one or two triangles. This tool covers the three cases that always have exactly one answer.
Which side is opposite which angle?
Side a is opposite angle A, and so on.
Is anything uploaded?
No. Your input stays in your browser and is never sent anywhere.