Updated Geometry

Triangle Calculator

Solve any triangle: sides, angles, area, perimeter, right triangles, and coordinate-based triangles in one multi-mode calculator.

Side & Angle Solver Area & Perimeter Right Triangle Coordinates

All-in-One Triangle Calculator

Switch between side and angle solving, area and perimeter, right triangle mode, Heron's formula, and coordinate geometry.

Enter any valid combination of at least three values (including at least one side). The calculator uses the law of cosines and law of sines to solve the triangle. SSA ambiguous cases are partially supported; if no unique solution is found, you will see an error.

Provide three sides for perimeter and Heron's formula area. You can also enter base and height separately for ½ × base × height.

Enter any two of: legs a and b, one leg and hypotenuse, or one angle A and one side. The calculator assumes C = 90° and A opposite side a.

Heron's formula works with three side lengths. The triangle must satisfy the triangle inequality for a real area to exist.

Coordinate mode treats the triangle vertices as A(x₁,y₁), B(x₂,y₂), C(x₃,y₃). It computes side lengths, perimeter, area using the shoelace formula, and the centroid.

Triangle Calculator – Complete Geometry Tool

This Triangle Calculator lets you solve side lengths, angles, area, perimeter, right triangles, and coordinate triangles in one place. It is useful for homework, engineering, construction, and quick geometry checks.

Side and Angle Solver

The Side & Angle Solver tab uses the law of cosines and the law of sines. You can provide at least three values, including at least one side, and the tool attempts to solve the remaining sides and angles. It supports common cases such as SSS, SAS, ASA, and AAS.

Area and Perimeter

The Area & Perimeter tab works both with three sides and with a base and height. From three sides it uses Heron's formula. When you enter base and height, it uses the standard formula ½ × base × height.

Right Triangle Mode

Right triangle mode assumes one angle is 90°. You can supply any two of a leg, another leg, the hypotenuse, or an acute angle and the calculator finds the rest, using the Pythagorean theorem and basic trigonometry.

Heron's Formula Mode

Heron's formula is valuable when all three sides are known and no angles are given. The calculator checks if the triangle is valid and then computes semiperimeter and area.

Coordinate Triangle Mode

Coordinate geometry mode uses three points in a plane. It calculates side lengths from distances between points, the perimeter, the area using the shoelace formula, and the centroid. This is helpful for analytic geometry and vector problems.

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