Trapezoid Area Calculator

How it is calculated

The area is the average of the two parallel sides multiplied by the height: A = (a + b) ÷ 2 × h. Here a and b are the lengths of the two parallel sides (bases) and h is the perpendicular distance between them, all in the same length unit. The result is in the square of that unit and is rounded to two decimals; the tool prints only the number, so you add the unit. All three values must be greater than zero, otherwise nothing is shown. The order of a and b does not matter. The slanted legs are not used, which is why the sloping side length is not an input.

Common mistakes

• Entering the slanted side as the height. The height is measured at a right angle between the two bases, not along a leg.
• Using two sides that are not parallel. Only the parallel pair counts as a and b; the other two sides are the legs.
• Mixing units, such as bases in meters and height in centimeters. Convert everything to one unit first.
• Forgetting to divide the sum by 2. Multiplying (a + b) by h gives double the true area.
• Reading the result as a perimeter or in linear units. It is an area, so the unit is squared.