Triangle Calculator

Solve any triangle from three known measurements — sides, angles, or a mix of both — and get every derived value: the missing sides and angles, area, perimeter, heights, inradius, circumradius, a classification (equilateral/isosceles/scalene, acute/right/obtuse), and a labeled diagram.

Supported configurations

• SSS — three sides. Solved with the law of cosines.
• SAS — two sides and their included angle. The third side follows from the law of cosines; the remaining angles from the law of sines.
• ASA / AAS — two angles and any one side. The third angle follows from the 180° angle sum; the remaining sides from the law of sines.
• SSA — two sides and a non-included angle. This is the classically ambiguous case: depending on the values, zero, one, or two valid triangles exist. When two solutions exist, both are shown labeled "Solution 1" and "Solution 2".

Enter any 3 values (with at least one side) and the calculator detects which configuration you've supplied.

What you get

• Every side and angle, in degrees or radians (your choice)
• Area (via Heron's formula), perimeter
• The three heights (altitudes) dropped from each vertex
• Inradius and circumradius
• Side-based classification (equilateral / isosceles / scalene) and angle-based classification (acute / right / obtuse)
• A scaled SVG diagram with labeled sides and angles

How to use it

1. Enter any three known values across the side and angle fields (at least one must be a side length).
2. Pick degrees or radians for angle inputs/outputs.
3. Read off the solved triangle, or copy the SVG diagram source.

All calculations run in your browser — nothing is uploaded.

Why do I sometimes get two solutions?

That's the SSA ("side-side-angle") ambiguous case: two sides and a non-included angle can, for some values, form two genuinely different triangles that both satisfy the same inputs. The calculator shows both when that happens.

What if my inputs don't form a valid triangle?

The calculator checks the triangle inequality (no side may be longer than the sum of the other two) and that angles sum to 180°, and reports exactly why a triangle can't be formed if either check fails.