Triangle Calculator
Solve a triangle — find its unknown sides, angles and area.
Completing a triangle
Given enough information about a triangle — some combination of its sides and angles — the rest can be worked out. This solves a triangle from what you know, finding the missing sides, angles and the area.
Enter the sides and angles you know to solve the triangle.
The rules that solve any triangle
For right triangles, the Pythagorean theorem and basic trigonometry handle everything. For any triangle, two powerful rules take over: the law of sines relates sides to the angles opposite them, and the law of cosines generalises the Pythagorean theorem to non-right triangles. Between them, these let you solve a triangle from various starting points — two sides and an angle, two angles and a side, or all three sides. One subtlety worth knowing is that certain combinations can give two valid triangles, an ambiguous case that catches people out. Triangles are fundamental to everything from navigation and surveying to computer graphics, all built on these few rules for turning partial information into a complete shape.
Questions & answers
What do I need to solve a triangle?
Enough of a combination of sides and angles — such as two sides and an angle, two angles and a side, or all three sides.
What rules are used for non-right triangles?
The law of sines, relating sides to opposite angles, and the law of cosines, which generalises the Pythagorean theorem to any triangle.
Is anything uploaded?
No. The calculation happens in your browser.