Math calculator

Triangle Calculator Formula Guide

Calculate triangle area, perimeter, and angles from three side lengths.

FormulaArea = sqrt(s x (s - a) x (s - b) x (s - c)), where s = perimeter / 2

Formula

Heron's formula

Area = sqrt(s x (s - a) x (s - b) x (s - c)), where s = perimeter / 2

A 3-4-5 triangle has area 6 and perimeter 12.

FAQ6 common questions for this calculator.

FAQs

What if the sides cannot form a triangle?+

The calculator returns zero area and marks the triangle as invalid.

How are the angles found?+

Angles are estimated with the law of cosines.

How does the Triangle Calculator calculate the result?+

For the Triangle Calculator, it uses the Heron's formula: Area = sqrt(s x (s - a) x (s - b) x (s - c)), where s = perimeter / 2. A 3-4-5 triangle has area 6 and perimeter 12.

What information do I need to use the Triangle Calculator?+

For the Triangle Calculator, enter three side lengths. Keep the units consistent with the calculator fields and compare your setup with the worked example on the page.

How accurate is the Triangle Calculator?+

Triangle Calculator is mathematically reliable for the entered values and selected operation. It follows the Heron's formula. Rounding, order of operations, and undefined cases can still affect interpretation.

What should I check before using the Triangle Calculator result?+

For the Triangle Calculator, check three side lengths, operation order, rounding precision, and undefined cases before using the result. Compare one changed value at a time when testing scenarios.

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Math guide

How to use the Triangle Calculator

Calculate triangle area, perimeter, and angles from three side lengths. The page also explains the heron's formula and shows a practical example: A 3-4-5 triangle has area 6 and perimeter 12.

  1. 1

    Enter your details

    Enter three side lengths, then complete any other fields shown in the calculator.

  2. 2

    Check the calculation

    Review the result alongside the heron's formula: Area = sqrt(s x (s - a) x (s - b) x (s - c)), where s = perimeter / 2.

  3. 3

    Compare scenarios

    Change one or more inputs to see how they affect the triangle Calculator result before you use the estimate.