Math

Triangle Calculator

Solve area, perimeter, and angles from three side lengths.

Inputs

Defaults are prefilled so the result is visible immediately.

Side a

Side b

Side c

Results

Results update as the calculator inputs change.

Area

Perimeter

Angle A

36.87 deg

Angle B

53.13 deg

Angle C

90 deg

Formula and Assumptions

Heron's formula gives area; law of cosines gives the three angles.

The triangle inequality must hold before area and angle results are meaningful.

Angles are derived with the law of cosines.

Reference Upgrade

Built from the Calculator.net model, with added context.

Live validation and instant result updates instead of a submit-only workflow.

Multiple decision metrics are shown together, not only the primary answer.

Formula notes and assumptions are visible on the page so the math is easier to audit.

Reference Model

Modeled after the input style and primary output on Calculator.net's Triangle Calculator.

The page keeps the math in one place and exposes the assumptions beside the result.

Default inputs: sideA=3, sideB=4, sideC=5