Trapezoids and triangles are two geometric shapes. A triangle is any three-sided figure. A trapezoid is a four-sided figure with one pair of parallel lines. You might want to calculate the area of a triangle or trapezoid if you had a room in that shape and you wanted to put down new carpeting. To figure the area of a triangle, you need to know the base and the height. To figure the area of a trapezoid, you need to know the length of the bases and the height.
Select one side of the triangle as the base and measure the length of that side.
Measure the perpendicular distance from the base to the top of the triangle to find the height.
Multiply the base times the height and divide the result by 2 to find the area of the triangle. For example, if your base equals 6 inches and your height equals 9 inches, multiply 6 times 9 to get 54 and divide 54 by 2 to get 27 square inches.
Measure the length of the two parallel sides of the trapezoid and the distance between those two sides. The distance between the two sides is the height.
Add the lengths of the two parallel sides and divide the result by 2. For example, if your sides are 12 inches and 14 inches long, add 12 to 14 to get 26 and divide by 2 to get 13.
Multiply the Step 2 result by the height of the trapezoid to find the area. Finishing the example, if the height equals 8 inches, multiply 8 by 13 to get 104 square inches as the trapezoid area.