Free Obtuse Triangle Calculator

An Obtuse Triangle Calculator is a free online tool that combines two essential functions: it works as a triangle type checker (detecting obtuse, acute, or right triangles) and also provides a reliable obtuse triangle area calculation. By using this obtuse angle detector, you skip the manual angle checks and formula substitutions—the tool processes your inputs and delivers immediate results.

Defining an Obtuse Triangle

A triangle is classified as obtuse when it contains exactly one interior angle that measures more than 90° (the obtuse angle), while the other two angles are acute (each less than 90°). This places the obtuse triangle in the oblique triangle category—triangles that do not contain a right angle. The presence of that single large angle is the clear distinction from an acute triangle, where all three angles are below 90°.

Determining Obtuse Status

To decide whether a triangle is obtuse, examine its angles. If any known angle exceeds 90°, the triangle is obtuse. When only two angles are given, you can find the third using the triangle‑sum theorem:

$$\alpha = 180^{\circ} - \beta - \gamma$$

Once the missing angle is calculated, simply check for a value greater than 90°. The triangle type checker performs this logic instantly for you.

Area Formulas for Obtuse Triangles

The same area equations used for any triangle work perfectly for obtuse triangles as well. Three common methods are available:

Base–Height formula (requires a base and its corresponding height):

$$\text{Area} = \dfrac{1}{2} \times \text{base} \times \text{height}$$

Heron’s formula (ideal when all three side lengths $a$, $b$, $c$ are known):
Let $s = \dfrac{a + b + c}{2}$ (semi‑perimeter). Then

$$\text{Area} = \sqrt{s\,(s - a)\,(s - b)\,(s - c)}$$

Side–Angle–Side formula (uses two sides and the included angle $\gamma$):

$$\text{Area} = \dfrac{1}{2} \times a \times b \times \sin(\gamma)$$

All three approaches yield correct results for obtuse triangles, so you can pick the one that matches the dimensions you have most readily available.

How the Obtuse Triangle Calculator Works

Using this tool is straightforward:

• To classify: Provide one, two, or three known angles. The obtuse angle detector instantly reports whether your triangle is obtuse (if at least one angle > 90°) or not.
• To calculate area: Enter the side lengths and, when needed, an angle. Then choose the preferred area formula. The calculator returns the obtuse triangle area along with the type classification.

The interface is designed for speed and simplicity, making the triangle type checker useful for students, teachers, and professionals who regularly work with triangle geometry.

Why It’s Practical

By bringing together angle classification and area calculation in one free web‑based tool, this obtuse triangle calculator removes repetitive manual steps. Whether you need to confirm triangle type or compute its area, you obtain accurate results without having to juggle multiple formulas.

Note that all three area formulas remain valid even when the triangle is acute or right‑angled; the classification feature, however, is specifically tuned to pinpoint obtuse triangles. This dual‑function approach saves time and reduces the chance of calculation errors.