How to use the Triangle Area Calculator
Enter the base and the perpendicular height in the same unit. The area comes back in square units.
Worked example
A triangle with a 10 cm base and a 6 cm height has an area of 10 × 6 ÷ 2 = 30 cm². A triangle is exactly half of the rectangle with the same base and height, which is where the divide by two comes from.
When you only know the sides
Use Heron’s formula. Add the three sides and halve the total to get s, then the area is √(s × (s − a) × (s − b) × (s − c)). For sides 5, 5 and 6, s is 8 and the area is √(8 × 3 × 3 × 2) = √144 = 12.
The formula
Area = base × height ÷ 2
Examples
- Base 8, height 10
Area: 40
- Base 14.5, height 6
Area: 43.5
- Base 3, height 4
Area: 6
Limitations and assumptions
Needs the perpendicular height. If you only know the three side lengths, use Heron’s formula instead.
Frequently asked questions
What is the triangle area formula?
Area = ½ × base × height.
What if I only know the three sides?
Use Heron's formula, which needs the semi-perimeter.
Does it work for any triangle?
Yes, as long as the height is perpendicular to the base.
How do I get a right triangle hypotenuse?
Use the Pythagorean theorem calculator.