How to use
- Enter the two parallel bases.
- Enter the perpendicular height.
- Read the area.
Formula
Area is the average of the two parallel bases, times the perpendicular height: (a + b) ÷ 2 × h. The two bases do not have to be equal. The result is rounded to four decimal places. A negative input is treated as zero.
Worked example
The fields open at bases 10 and 6, and height 4. The average base is 8. Area is 8 × 4 = 32. Swapping the two bases does not change the area. If the bases were both 8, the shape would be a parallelogram, or a rectangle if the sides are perpendicular, and the area would still be 32.
How to read the result
32 is the area between the two parallel sides. It is not the perimeter, and it does not tell you the slanted side lengths. A taller trapezoid with the same bases has a larger area in direct proportion to the height.
When this does not apply
Height must be perpendicular to the two bases, not the length of a slanted side. If the two given lengths are not parallel, this formula does not describe the shape. The page does not solve for a missing base or a missing height.