What is Triangle Calculator?
Triangle Calculator — A triangle calculator solves missing sides, angles, area, perimeter, heights, medians, inradius, and circumradius from known triangle measurements.
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Free triangle solver supporting SSS, SAS, ASA, AAS, and SSA methods. Compute triangle area using Heron's formula, base-height, or SAS; find all unknown angles via the Law of Cosines and Law of Sines; calculate perimeter, semiperimeter, heights, medians, inradius, circumradius, and classify triangle type (equilateral, isosceles, scalene, right, obtuse).
Triangle Calculator: Enter the triangle values you know, such as three sides, two sides and an angle, or two angles and a side. The calculator solves the missing sides and angles and returns area, perimeter, triangle type, and related geometry values.
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Triangle Calculator — A triangle calculator solves missing sides, angles, area, perimeter, heights, medians, inradius, and circumradius from known triangle measurements.
Choose Solving Method: Select SSS (three sides), SAS (two sides + included angle), ASA (two angles + included side), AAS (two angles + non-included side), or SSA (two sides + non-included angle) based on your known values.
Enter Known Values: Input side lengths in any unit and angles in degrees or radians. The calculator validates inputs against the Triangle Inequality Theorem before solving.
Calculate All Properties: Click 'Calculate' to find all unknown sides, angles, area (via Heron's formula, base-height, or SAS), perimeter, semiperimeter, heights, medians, inradius, and circumradius.
Analyze Results: Review the triangle type classification (equilateral, isosceles, scalene, right, obtuse, acute), copy individual values, and access calculation history for comparison.
Geometry Homework: Solve SSS, SAS, ASA, AAS, and SSA triangle problems with step-by-step results for high school and college geometry courses.
Structural Engineering: Analyze truss systems, beam load triangles, and stress distribution using the Law of Cosines and Law of Sines.
Surveying & Land Measurement: Calculate unknown distances and bearings between survey points using triangulation methods.
Architecture & Construction: Design roof pitch angles, rafter lengths, stairway stringers, and gable framing with precise triangle geometry.
Computer Graphics & Game Development: Compute triangle areas and angles for 3D mesh rendering, collision detection, and polygon tessellation.
Navigation & Physics: Apply triangle calculations to vector decomposition, force diagrams, projectile trajectories, and bearing-distance problems.
| Type | Definition | Key Properties |
|---|---|---|
| Equilateral | All 3 sides are equal | All angles are 60° |
| Isosceles | 2 sides are equal | Base angles are equal |
| Scalene | No equal sides | No equal angles |
| Right | Has one 90° angle | Follows Pythagoras (a² + b² = c²) |
| Obtuse | One angle > 90° | Sum of other two angles < 90° |
"Not every set of three lines can form a triangle. The Triangle Inequality Theorem states that the sum of the lengths of any two sides must be greater than the length of the third side. If Side A = 5 and Side B = 3, Side C cannot be 9, because 5 + 3 is not greater than 9. This is a fundamental check in all geometry engines."
— FastTools Geometry Team
Advanced triangle calculations
Instructions:
Provide 3 values including at least one side. When radians are selected, angles can be entered as π/2, π/4, etc.