Trapezoid Calculator
Enter both parallel sides and the height below to instantly get the area, plus the perimeter if you add the two legs.
Optional — add both legs to also get the perimeter:
Trapezoid Formulas
Area = ((a + b) / 2) × h. Perimeter = a + b + c + d, where c and d are the two legs.
A common mistake is treating one of the slanted legs as the height. Height has to be the perpendicular distance between the two parallel sides — measured straight up and down — not the length along a slanted leg, unless that leg happens to meet a base at a right angle.
Worked example
A trapezoid with parallel sides 8 and 14, and height 5.
Area = ((8 + 14) / 2) × 5 = 11 × 5 = 55
A second example, with parallel sides 6 and 10, and height 4.
Area = ((6 + 10) / 2) × 4 = 8 × 4 = 32
Keep going
- A trapezoid's area formula is a triangle's area formula averaged over two parallel sides instead of one; the triangle area calculator shows that simpler base case. Triangle Area Calculator
Frequently Asked Questions
What is the formula for the area of a trapezoid?
Area = ((a + b) / 2) × h, where a and b are the two parallel sides and h is the perpendicular height between them.
What is the formula for the perimeter of a trapezoid?
Perimeter = a + b + c + d — simply add up all four sides, including the two non-parallel legs.
What's the difference between a trapezoid and a parallelogram?
A trapezoid has exactly one pair of parallel sides. A parallelogram has two pairs of parallel sides (both pairs), which is a stricter condition.
What is the midsegment of a trapezoid?
The midsegment (or median) connects the midpoints of the two legs. It's always parallel to both bases, and its length is exactly the average of the two parallel sides — (a + b) / 2 — which is also why the area formula works out to midsegment length times height.
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