Triangle Calculator
Area = √(s(s−a)(s−b)(s−c)) where s = (a+b+c)÷2 (Heron's formula)s=6; area=√(6×3×2×1)=√36=6; perimeter=12
Free online tool
Triangle Calculator
Enter the lengths of all three sides to find area and perimeter.
Instant calculation
Triangle Calculator
Enter the lengths of all three sides to find area and perimeter.
Your result
Calculation
Your numbers stay in this browser. Nothing is uploaded or saved.
Three clear steps
How to use this calculator
- 01
Enter side A
Type the length of the first side.
- 02
Enter side B
Type the length of the second side.
- 03
Enter side C
Type the length of the third side.
The formula
How this calculation works
Heron's formula works for any triangle when all three side lengths are known.
Check the method
Worked examples
Each example follows the same formula used by the calculator.
Triangle sides 3, 4, 5 — area and perimeter?
s=6; area=√(6×3×2×1)=√36=6; perimeter=12Area=6, Perimeter=12Common questions
Questions about this calculation
What is the Triangle Calculator?
The Triangle Calculator helps you calculate the area and perimeter of a triangle from its three sides. Enter your values and select Calculate to get an instant result.
How is the result calculated?
Heron's formula works for any triangle when all three side lengths are known.
Can you show an example?
Example: Triangle sides 3, 4, 5 — area and perimeter? — Area=6, Perimeter=12.
Is my data saved when I use the Triangle Calculator?
No. All calculations run locally in your browser. Your inputs and results are never uploaded, stored or shared with anyone.
Is the Triangle Calculator free to use?
Yes. The Triangle Calculator is completely free. No account, sign-up or payment is required. It works on mobile, tablet and desktop.
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