Trapezoid Area Calculator
The area of a trapezoid from its two parallel sides and height.
Result
Area
26.00
How it works
A trapezoid is a quadrilateral with two parallel sides — the bases a and b. Its area is the average of the bases times the height: A = (a + b)/2 × h. Intuition: averaging the two bases turns the slanted shape into an equivalent rectangle of the same height. The crucial detail is the height: it is the perpendicular distance between the two parallel sides, never the length of a slanted leg. On a drawing, it is the length of a line dropped at a right angle from one base to the other. With bases of 8 and 5 and a height of 4, the area is (8+5)/2 × 4 = 26. The shape appears in land parcels, roof cross-sections, channels and ramps — anywhere two edges run parallel but differ in length.
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Frequently asked questions
Which sides are a and b?
The two parallel sides; the height is the perpendicular distance between them, not the slanted side.
What units does it use?
Whatever you enter: lengths in metres give an area in square metres.
What if my quadrilateral has no parallel sides?
Then it is not a trapezoid and this formula does not apply. Split the shape into two triangles (or use coordinates) and add the pieces' areas.
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