Triangle calculators

Triangle Solver with Steps

Choose what you know and get a step-by-step triangle solution.

Missing sidesAnglesArea & perimeterStep-by-step formula path

Calculate triangle values

Enter the known values for this triangle case. Results are educational estimates for geometry and measurement problems.

Result

What this calculator does

This calculator is designed for common triangle homework, geometry, construction, and measurement problems where you know some sides or angles and need the rest.

SSS, SAS, ASA, AASUse the right case for the information you know.
Steps matterThe page explains which formula was used.
Related pagesUse a dedicated page for missing sides, right triangles, or angles.
For classroom work, check the required rounding rules and whether angles are in degrees or radians. This page uses degrees.

Triangle solver cases covered on this page

A full triangle solver tries to complete the triangle from the known values. Most classroom and measurement problems fall into one of these cases.

CaseKnown valuesMain method
SSSThree sidesLaw of Cosines, then Heron’s formula
SASTwo sides and included angleLaw of Cosines first
ASATwo angles and included sideAngle sum rule + Law of Sines
AASTwo angles and a non-included sideAngle sum rule + Law of Sines
Right triangleTwo sidesPythagorean theorem + trigonometry

How the step-by-step solution is built

  1. Validate the inputs. Side lengths must be positive, angles must make sense, and side combinations must pass triangle inequality.
  2. Identify the case. The calculator chooses SSS, SAS, ASA, AAS, SSA, or right triangle logic based on the selected mode.
  3. Solve the missing values. It uses the law of cosines, law of sines, Pythagorean theorem, or angle sum rule.
  4. Calculate extra values. After sides and angles are solved, it can estimate area, perimeter, semiperimeter, and triangle type.

SSA warning: why some triangle problems have two answers

The SSA case can be ambiguous. If you know two sides and a non-included angle, the given information may describe one triangle, two possible triangles, or no triangle. That is why this calculator explicitly labels the SSA case rather than hiding it inside a general result.

For homework, always check whether your teacher expects the ambiguous SSA case to be discussed. A single numeric result may not be enough.

Best use cases

Homework checkingVerify side, angle, area, and perimeter results after solving by hand.
Measurement planningEstimate missing lengths when a triangular layout can be described by sides and angles.
Formula selectionLearn whether the problem needs Pythagorean theorem, law of sines, or law of cosines.

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