The area of a triangle tells you how much surface it covers. The standard formula uses the base and the height, and there are alternatives when you only know the side lengths.
What you'll need
- A ruler or measurements
- A calculator (optional)
Step by step
- Identify the basePick any one side of the triangle to serve as the base and note its length.
- Measure the heightFind the perpendicular height, which is the straight distance from the base to the opposite corner, measured at a right angle to the base.
- Multiply base by heightMultiply the base length by the height. For a base of 6 and a height of 4, that gives 24.
- Divide by twoDivide that product by 2 to get the area. In the example, 24 divided by 2 gives an area of 12 square units.
- Label the unitsWrite the answer in square units, such as square centimeters or square inches, matching the units you measured with.
Handy tips
- The height must be perpendicular to the base, not the length of a slanted side.
- For a right triangle, the two sides that meet at the right angle are the base and height.
- If you only know all three sides, Heron's formula lets you find the area without the height.
FAQ
What is the formula for the area of a triangle?
Area equals one half times the base times the height, often written as A = 1/2 x b x h.
What if I do not know the height?
If you know all three side lengths, use Heron's formula. If you know two sides and the angle between them, use one half times a times b times the sine of that angle.
Does it matter which side I call the base?
No. Any side can be the base as long as you use the height measured perpendicular to that same side. The area comes out the same.