Math calculator
Triangle Calculator
Calculate triangle area, perimeter, and angles from three side lengths.
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.
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?+
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?+
Calculate triangle area, perimeter, and angles from three side lengths.
How accurate is the Triangle Calculator?+
Triangle Calculator applies the formula and assumptions shown on this page. Results may be rounded for readability, so verify changing rates, thresholds, medical guidance, or legal rules with the cited source or a qualified professional.
What should I check before using the Triangle Calculator result?+
Check that the units, dates, rates, and assumptions match your situation. Change one input at a time to understand which values have the largest effect on the result.
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
Enter your details
Enter three side lengths, then complete any other fields shown in the calculator.
- 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
Compare scenarios
Change one or more inputs to see how they affect the triangle Calculator result before you use the estimate.
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