Triangle Calculator

Solve any triangle from three known values and get all three sides, all three angles, the area and the perimeter.

Triangle calculator

What do you know?

Side a

Side b

Side c

Sides: —

Angles: —

Area: — · Perimeter: —

Angles are entered and shown in degrees. Side a is opposite angle A, b opposite B and c opposite C.

Pick the set of values you already know: three sides, two sides and an angle, or two angles and a side.
Type the three numbers into the boxes, using degrees for any angle.
Read the missing sides, all three angles, the area and the perimeter.

Common questions about the free online triangle calculator.

Choose the three sides mode, enter a, b and c, and the angles come from the law of cosines while the area comes from Heron's formula.

Use it when you know two sides and the angle between them. Enter side b, side c and angle A and the third side follows from the law of cosines.

It means two angles and the side between them. Enter angles A and B and side c, and the remaining sides come from the law of sines.

For a valid triangle any two sides must add up to more than the third. If they do not, the tool says the sides cannot form a triangle.

Angles are entered and displayed in degrees. If your values are in radians, multiply them by 180 and divide by pi first.

The area uses Heron's formula from the three sides, so it is accurate for any triangle once all the sides are known.

Sides, area and perimeter are rounded to six decimal places, while angles are shown to two decimal places.

No. All of the trigonometry runs locally in your browser, so nothing you enter is ever transmitted.

Yes. The triangle calculator is completely free and unlimited, with no account required and no hidden charges.

Last updated: October 10, 2026