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geometryClassic tool

Triangle Calculator

Calculate area, perimeter, semiperimeter, angles, and triangle type from three side lengths.

Use this triangle calculator to quickly find area, perimeter, semiperimeter, interior angles, and triangle classification from three side lengths. It is useful for homework, geometry review, measurement checks, and fast verification when you do not want to rework every step by hand.

After entering sides A, B, and C, the tool first checks whether the values actually form a triangle. If they do, it applies Heron’s formula for the area, computes the three angles in degrees, and classifies the figure as equilateral, isosceles, or scalene, as well as acute, right, or obtuse.

This is helpful for school math, drafting, light design work, and practical geometry tasks. If you want to confirm whether a 3-4-5 triangle is right or compare other dimensions quickly, the result appears in a clean, readable summary.

The calculator uses the three sides to validate the triangle and return the key measurements in one pass.

Classic example: 3, 4, and 5 form a right triangle.

SummaryEnter all three sides to calculate the triangle.
Perimeter—
Area—
Semiperimeter—
Interior angles—
Type by sides—
Type by angles—
Applied formulas = (a + b + c) / 2; area = √(s(s-a)(s-b)(s-c))

Use clear inputs to get a more useful result.