Area of a Triangle Calculator
Any triangle is exactly half of a parallelogram with the same base and height. The height must be perpendicular to the base, not a slanted side.
A = ½ × b × h
Perimeter: Needs all three sides — use the triangle calculator
- Perimeter
- see note
- A = ½ × b × h = ½ × 10 × 6 = 30 ft²
Area in other units
| m² | 2.7871 |
| cm² | 27,870.9 |
| ft² | 30 |
| in² | 4,320 |
| yd² | 3.3333 |
| acres | 0.000689 |
| hectares | 0.000279 |
How to find the area of a triangle
Formula: A = ½ × b × h. Perimeter: Needs all three sides — use the triangle calculator.
- Measure every length in the same unit. Mixing feet and inches is the most common mistake; convert first (6 in = 0.5 ft).
- Put the numbers into the formula above. The calculator shows each substitution with your numbers.
- Area comes out in square units (ft², m²). If you need a different unit, open "Area in other units".
Why a triangle is half of b × h
Slide the top corner sideways. The triangle leans, but its base and height stay the same, so its area never changes. Switch on the copy: two identical triangles always make a parallelogram of area b × h, so one triangle is half.
Area = ½ × 10 × 6 = 30 square units
Questions people ask
What if I only know the three sides?
Use Heron's formula: with s = (a + b + c) / 2, area = √(s(s−a)(s−b)(s−c)). The triangle calculator does this for you.
What if I know two sides and the angle between them?
Area = ½ × a × b × sin(C). This is the SAS mode in the triangle calculator.
Can the height fall outside the triangle?
Yes. In an obtuse triangle the perpendicular height from the top vertex lands on the extension of the base. The formula still works.
Stuck on a word problem?
Paste a homework question or describe your project. The AI tutor names the formula and works it through step by step. Always check the result with the calculator above.