Area of a Triangle: Formula and Examples
Learn the triangle area formula with two worked examples and the most common mistake.
The formula
- A = ½ × base × height
- Height is perpendicular to the base
A triangle is half of a rectangle (or parallelogram) with the same base and height.
Example 1
Find the area of a triangle with base 10 and height 6.
- A = ½ × 10 × 6
- A = 30
30 square units
Example 2
A right triangle has legs 5 and 12 and hypotenuse 13. Find its area.
- The legs are perpendicular, so use them as base and height
- A = ½ × 5 × 12 = 30
30 square units
Common mistake
A = ½ × base × slanted side
Height is the perpendicular distance, not a slanted side.
In a right triangle, the legs are the base and height. Never use the hypotenuse.
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