Calculate a triangle’s perimeter, area, angles, height, and type from three side lengths. The tool validates the triangle and shows the formula steps.
For a 3-4-5 triangle, the perimeter is 12, the area is 6 square units, and the angles are about 36.87°, 53.13°, and 90°.
Right scalene triangle
All calculations run locally in your browser. Your entered values are not sent to an external service.
How do I use the triangle calculator?
Enter the three side lengths and select Calculate Triangle. The calculator checks whether the sides form a valid triangle, then returns perimeter, area, angles, height, and triangle type.
Which triangle formulas are used?
The calculator uses perimeter P = a + b + c, semi-perimeter s = P / 2, Heron’s formula A = √s(s-a)(s-b)(s-c), and the law of cosines to estimate each angle.
How are triangle types identified?
| Type | Meaning |
|---|---|
| Equilateral | All three sides are equal. |
| Isosceles | Two sides are equal. |
| Scalene | All sides are different. |
| Right | One angle is 90°. |
| Acute | All angles are less than 90°. |
| Obtuse | One angle is greater than 90°. |
What are triangle calculation examples?
3-4-5 triangle
Sides 3, 4, and 5 form a right triangle. Its area is 6 and perimeter is 12.
5-5-5 triangle
Sides 5, 5, and 5 form an equilateral triangle. Each angle is 60°.
What triangle mistakes should I avoid?
Ignoring the triangle inequality
The sum of any two sides must be greater than the third side.
Confusing height with side length
Triangle area uses perpendicular height, not a slanted side unless the side is perpendicular to the base.
Rounding too early
Round the final answer, not the intermediate trigonometric values.
Triangle Calculator FAQs
Can three side lengths determine a triangle?
Yes, if the side lengths satisfy the triangle inequality. Then area and angles can be calculated.
How is triangle area found from three sides?
Use Heron’s formula with the semi-perimeter: A = √s(s-a)(s-b)(s-c).
How are triangle angles calculated?
The calculator uses the law of cosines for each angle.
Does this calculator support degrees?
Yes. The output angles are shown in degrees.
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Reviewer
This non-medical math content is reviewed under the SolverCalc reviewer rule by Prof. Dr. Khalil Mudassar. WordPress adds the author bio automatically, so this page does not include a duplicate author box.
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Disclaimer
This calculator is for educational geometry use. For engineering, surveying, construction, or legal measurements, verify dimensions and formulas with the required professional standard.