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Triangle Calculator

Find every side, angle and the area of a triangle from the measurements you know.

  • Free
  • No sign-up
  • Nothing is sent or stored
What do you know?

In ASA mode, c is the side between angles A and B.

Result

Area
6
Sides a, b, c
3, 4, 5
Angles A, B, C
36.8699°, 53.1301°, 90°
Perimeter
12
Type
Scalene, right
How it was calculated
  1. Angles from the law of cosines: cos A = (b² + c² − a²) ÷ 2bc
  2. Area by Heron's formula: s = 6, A = √(s(s−a)(s−b)(s−c))

The calculation happens instantly in your browser. The numbers you enter are not sent to our servers or saved.

How to use the Triangle Calculator

  1. Choose what you know: 3 sides, 2 sides and the angle between them, or 2 angles and the side between them.
  2. Enter the values.
  3. Read all sides and angles, the area and the triangle type.

What does this tool do?

Three measurements (including at least one side) fix a triangle. The calculator uses the law of cosines and law of sines to find the missing sides and angles, and Heron's formula for the area.

It also tells you whether the triangle is equilateral, isosceles or scalene, and acute, right or obtuse.

Why use it?

  • Three ways to solve.
  • Checks that the triangle can exist.
  • Classifies the triangle.

The formula

Law of cosines: c² = a² + b² − 2ab cos C
Law of sines: a ÷ sin A = b ÷ sin B = c ÷ sin C
Heron: A = √(s(s − a)(s − b)(s − c)), s = (a + b + c) ÷ 2

Privacy

The calculation happens instantly in your browser. The numbers you enter are not sent to our servers or saved. There's no account to create and nothing to install.

Last reviewed by the M2Toolkit team.

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