How to Calculate Area of a Triangle. Whether you're carpeting a room, hanging wallpaper or shingling a roof, you may need to calculate the area of a triangle. Knowing the correct formula will make your job easier and save you time by avoiding mistakes. If it's been a while since your last math class, you may need help remembering how to calculate the area of a triangle.
Use the formula base (b) times height (h) divided by 2 to calculate the area of a triangle (b x h / 2).
Choose any side of the triangle as the base. If it's right triangle, use one of the sides forming the right angle.
Measure the length of the base.
Find the height of the triangle. The height is not necessarily one of the triangle's sides. The height will always be at a right angle, or perpendicular, to the base. Measure the height.
Multiply the base times the height.
Take the number that you calculated in Step 5 and divide it by 2. This will give you the area of the triangle, or the total square measurement.
Create a basic diagram of the triangle to help you visualize the base side and height of the triangle.