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Triangle Calculator

Solve any triangle from 3 sides, 2 sides and an angle, 2 angles and a side, or a right triangle's legs. Get every side, angle, the area and perimeter.

Area
6
Side a
3
Side b
4
Side c
5
Angle A
36.8699°
Angle B
53.1301°
Angle C
90°
Perimeter
12
Type
Scalene, right
Height to side c
2.4

Solve a triangle from three facts

A triangle is fixed by three measurements, as long as at least one is a side. From three sides, the law of cosines gives the angles; from two angles and a side, the law of sines gives the other sides; for a right triangle, Pythagoras gives the hypotenuse (3, 4, 5). The area comes from Heron's formula: the classic 3-4-5 right triangle has an area of 6 and a perimeter of 12. The calculator also tells you whether the triangle is equilateral, isosceles or scalene, and acute, right or obtuse.

How to use it

  1. 1

    Choose what you know

    3 sides, 2 sides + angle, 2 angles + side, or right triangle.

  2. 2

    Enter the values

    Angles in degrees.

  3. 3

    Read the solution

    All sides and angles, area, perimeter and type.

Frequently asked questions

What is the Pythagorean theorem?

In a right triangle, a² + b² = c², where c is the hypotenuse.

How do I find the area from three sides?

Heron's formula: s = (a + b + c) ÷ 2, area = √(s(s − a)(s − b)(s − c)).

Why can't some sides form a triangle?

Each side must be shorter than the other two added together.

Is anything stored?

No. The calculation runs in your browser.

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