Triangle Area Calculator
Solve any triangle from three known values — SSS, SAS, ASA, AAS or SSA — and get every side, every angle, the area, the perimeter and the heights, with the law of sines and cosines steps written out and a scaled diagram.
Processed entirely in your browser — nothing you enter here is ever uploaded.
Result
About this tool
This page opens the triangle calculator with the area as the headline result. Enter three sides and the area comes from Heron's formula — s = (a + b + c)/2, then √(s(s−a)(s−b)(s−c)) — or switch to a case with a known angle and the calculator uses ½·a·b·sin C instead. Either way the formula and the substituted numbers are printed as explicit steps.
The default 3-4-5 example gives an area of exactly 6: the semi-perimeter is 6, and √(6·3·2·1) = √36 = 6. Because 3-4-5 is a right triangle, the same number also falls out of the shortcut ½·3·4 — a handy way to see that both methods agree before you trust the tool with messier sides.
Alongside the area you still get the full solution: every angle, the perimeter and the three heights, which follow directly from the area as h = 2·Area/side. That makes this page useful for land-plot estimates, fabric and material cutting, geometry homework and any task where the area is the number you actually came for.
Example. Sides 3, 4, and 5 produce a right angle opposite the side of length 5, area 6, and perimeter 12.
Limit. SSA can return two triangles, one triangle, or none, and angles are degrees.