Area = 84
Triangle Calculator
Use this free triangle calculator to enter three sides and find area with Heron's formula, perimeter, semiperimeter, angles, side type, and angle type.
Formula steps Examples included Copy results Private history
scalene acute triangle84 cm^2
- Perimeter
- 42 cm
- Semiperimeter
- 21 cm
- Angles
- 53.1301023542 degrees, 59.4897625939 degrees, 67.380135052 degrees
Steps
- Check the triangle inequality: each pair of sides must add to more than the third side.
- Find semiperimeter: (13 + 14 + 15) / 2 = 21.
- Use Heron's formula: area = sqrt(s(s-a)(s-b)(s-c)).
- The area is 84 cm^2. Angles are found with the law of cosines.
How to use the triangle calculator
- Enter the three side lengths of the triangle.
- Add an optional unit label such as cm, m, or in.
- Press Calculate triangle to find area, perimeter, angles, and triangle type.
- Use examples, recent answers, or copy the result while checking geometry work.
Common uses
Find the area of a triangle when you know all three side lengths.
Check whether side lengths form a valid triangle.
Estimate triangle angles with the law of cosines.
Classify triangles as scalene, isosceles, equilateral, acute, right, or obtuse.
Examples
Area = 6
Area = 31.2249899919
Frequently asked questions
Quick answers about formulas, units, valid measurements, examples, copying, and private in-browser history.
What can I use the Triangle Calculator for?
Use it to calculate triangle area, perimeter, semiperimeter, angles, and triangle type when you know all three side lengths.
What formula does the Triangle Calculator use?
It uses Heron's formula for area: s = (a + b + c) / 2, then area = sqrt(s(s-a)(s-b)(s-c)). Angles are estimated with the law of cosines.
Can any three numbers make a triangle?
No. The sides must pass the triangle inequality: each pair of sides must add to more than the third side.
Does this replace a right triangle calculator?
Use this tool for any triangle from three sides. Use the Right Triangle Calculator or Pythagorean Theorem Calculator when the triangle is known to have a 90-degree angle.
How should I enter units?
Enter the same length unit for every side. The calculator reports perimeter in that unit and area in square units.
Is my triangle history private?
Yes. Recent triangle answers stay only in the current browser tab while you use the page. They are not sent to a server.