Search a tool
en

Triangle

Work out the area, perimeter and largest angle of a triangle from its three side lengths. Locally, no upload.

This calculator gives a non-binding, model-based estimate and is not financial, tax or legal advice. More in the disclaimer
Side a
Side b
Side c

Result

6
Area
12
Perimeter
90°
Largest angle
No upload100% local
Your content stays with youno third-party access
Servers in GermanyGDPR by design
Independently auditedTLS A+ · HTTP headers A+
Is my file uploaded?

No. Everything runs in your browser - your file never leaves your device. How this is verifiable

From the three side lengths of a triangle you can determine the area, perimeter and angles - without knowing the height. The area follows from Heron's formula (using half the perimeter), the perimeter is the sum of the sides, and the largest angle lies opposite the longest side and follows from the law of cosines. The largest angle tells you the type: exactly 90 degrees means right-angled, more than 90 obtuse, less acute.

The calculation runs entirely locally in your browser, in pure JavaScript - nothing is uploaded and nothing is stored. Three sides form a triangle only if each side is shorter than the sum of the other two (the triangle inequality). If that is not met, there is no valid triangle and the area is zero. The calculator is unit-free. Change a side and everything updates instantly.

An honest note: this is a pure calculation helper from three side lengths. It assumes the three sides form a valid triangle; otherwise the area is zero. Results are shown rounded to two decimals (the angle to one). Other kinds of input (such as two sides and an angle) are not supported.

Specifications

Specifications
Input formatsForm inputs (no file)
ProcessingLocally in your browser (JavaScript)
File uploadNone

In 3 steps

  1. Enter the three side lengths a, b and c.
  2. Make sure the combination is valid (the triangle inequality).
  3. Read off the area, perimeter and largest angle.

Limitations: A pure calculation helper from three side lengths: area by Heron, perimeter = a+b+c, largest angle by the law of cosines. Assumes a valid triangle (the triangle inequality); otherwise the area is zero. Unit-free. Rounded to two decimals (the angle to one).

FAQ

Are my inputs uploaded?

No. The calculation runs entirely locally in the browser (pure JavaScript); nothing is sent or stored.

Why do I get zero as the area?

Because the three sides do not form a valid triangle: each side must be shorter than the sum of the other two (the triangle inequality).

How is the area found without the height?

With Heron's formula: from half the perimeter and the three side lengths, without needing any height.

What does the largest angle tell me?

The type of triangle: exactly 90 degrees is right-angled, over 90 obtuse, under 90 acute. It lies opposite the longest side.

Related tools