Area of a Trapezoid Calculator
Find the area of a trapezoid from its two parallel sides and the perpendicular height using A = ½ × (a + b) × h. A trapezoid has one pair of parallel sides (the bases a and b); the height is the straight-line distance between them. Enter the two bases and the height to get the area in square units.
Formula
Area = ½ × (a + b) × h
- Add the two parallel sides (bases a and b), halve the sum to get their average, then multiply by the height.
- The height must be the perpendicular distance between the two parallel sides — not the length of a slanted side.
- If both bases are equal, the trapezoid is a parallelogram and the formula reduces to base × height.
- The area is in the square of the length unit you use; mix no units (all cm or all m).
Example: bases 5 and 7, height 4
Inputs
- Base a (first parallel side): 5
- Base b (second parallel side): 7
- Height (perpendicular distance): 4
With bases a = 5 and b = 7 and height h = 4, the area is ½ × (5 + 7) × 4 = ½ × 12 × 4 = 24 square units.
Frequently asked questions
What is the formula for a trapezoid's area?
A = ½ × (a + b) × h, where a and b are the parallel sides (bases) and h is the perpendicular height between them.
Which sides are the bases?
The bases are the two parallel sides. The other two (non-parallel) sides are the legs and are not used in the area formula.
What height should I use?
Use the perpendicular distance between the two parallel sides, not the length of a slanted leg.
What if the two bases are equal?
Then the shape is a parallelogram (or rectangle), and the formula simplifies to base × height.
What units does the area use?
The area is in the square of the unit you use for the sides and height. Lengths in metres give an area in square metres.