Triangle Calculator (Heron + ½bh)
Solve any triangle: area by Heron √(s(s−a)(s−b)(s−c)) or ½bh, perimeter and angles.
- Example: 3-4-5 cm → area 6 cm².
- Free online solver.
Figures are estimates from this calculator’s standard formula — adjust the inputs in the tool below for your exact number.
How the Triangle Calculator Works
With base and height use A = ½bh. With three sides use Heron: s = (3+4+5)/2 = 6 cm, so A = √(6·3·2·1) = 6 cm². With two sides and the included angle use A = ½ab·sin C. The tool also returns perimeter 12 cm and the right angle between the 3 and 4 cm legs.
- 1
Pick your known set
Base+height, three sides (SSS), or two sides with the angle between (SAS).
- 2
Enter the measurements
Any consistent unit — cm, m, ft, in.
- 3
Solve
Area, perimeter and missing angles come back instantly.
Use Cases
Land plots, roof faces and site surveying
Checking ramp and stairway triangular sections
Solving SSS, SAS and ASA textbook problems
Estimating fabric or tile for triangular surfaces
Tips
- 1
Heron needs no height — only the three sides
- 2
1 cm² area here means sides in cm; keep units uniform
- 3
The 3-4-5 triangle is the classic right-triangle check for corners
Common Mistakes
Using a slanted side as the height — h must be perpendicular to the base
Feeding Heron sides that violate a + b > c
Swapping the included angle with an exterior one in SAS
Mixing cm and m in one calculation
FAQs
Related tools
Pick another tool to continue your calculation.
Right Triangle Calculator (Pythagoras)
Calculate all sides and angles of a right triangle.
Golden Rectangle Dimensions Calculator (φ = 1.618)
Calculate golden rectangle dimensions.
3D triangle area from vertices Calculator
Calculate triangle area from 3D coordinates.
Rectangle Calculator (A = l×w)
Calculate rectangle area, perimeter, and diagonal online. Free rectangle calculator for geometry and construction. Find dimensions quickly and accurately.
Reuleaux triangle area Calculator (A = (π−√3)s²/2)
Calculate Reuleaux triangle area and perimeter.
Spherical Triangle Area Calculator (A = R²E)
Calculate triangle area on sphere surface.