Calculate the area of a trapezoid from its two parallel side lengths and the perpendicular distance between them. Choose US or metric inputs and see square feet, square yards and square meters. This is a flat-shape area calculation, not a survey, material order or structural design.
Trapezoid area from parallel sides and height
Height is measured at a right angle to the parallel sides, not along a sloping side. All entries use the selected unit. Changing units clears inputs and results.
Trapezoid area formula
Area = (parallel side A + parallel side B) × perpendicular height ÷ 2. Math Is Fun gives this formula for a trapezoid, with height perpendicular to the bases.1 The tool uses the sum of the parallel sides, not the sum of all four sides. Either parallel side can be entered as A; swapping A and B leaves the area unchanged.
Which sides and height should I enter?
The two bases must be parallel. Height is the perpendicular distance between their lines. A diagonal measurement or sloping leg is not interchangeable with that height. The calculator cannot confirm parallelism from three numbers and does not calculate an arbitrary four-sided area's shape from its side lengths. If you have only four side lengths, this form does not infer the missing perpendicular height.
Worked examples
- 10 ft and 20 ft bases, 8 ft height: (10 + 20) × 8 ÷ 2 = 120 sq ft, or 13.33333333 sq yd and 11.1483648 sq m.
- Equivalent metric inputs: 3.048 m and 6.096 m bases with 2.4384 m height give the same 120 sq ft and 11.1483648 sq m.
- 2 m and 4 m bases, 3 m height: (2 + 4) × 3 ÷ 2 = 9 sq m, or about 96.87519375 sq ft.
- 12 in and 24 in bases, 12 in height: 216 sq in = 1.5 sq ft. Area units are squared; divide square inches by 144, not by 12, to get square feet.
Trapezoid area chart
Calculated examples for stated parallel sides and perpendicular heights. These are not recommended dimensions or product coverage.
| Parallel side A | Parallel side B | Perpendicular height | Area |
|---|---|---|---|
| 6 ft | 10 ft | 4 ft | 32 sq ft |
| 8 ft | 12 ft | 5 ft | 50 sq ft |
| 10 ft | 20 ft | 8 ft | 120 sq ft |
| 12 ft | 18 ft | 10 ft | 150 sq ft |
| 20 ft | 30 ft | 12 ft | 300 sq ft |
US and metric conversion
NIST states that one inch is exactly 25.4 millimeters and gives 0.9144 meters per yard with 36 inches per yard.2 The tool uses 0.0254 meter per inch, 0.3048 meter per foot and 0.9144 meter per yard. Area conversion uses squared length factors. For example, square feet = square meters ÷ (0.3048 × 0.3048).
What the result does not include
The area covers one flat trapezoid. It does not include depth, material thickness, cutting waste, overlap, package yield or installation cost. For a larger shape, add only non-overlapping areas, or subtract overlap separately. A curved boundary is not automatically a straight-sided trapezoid. More displayed digits do not make measurements more accurate.
For other shapes, use the square footage calculator, triangle area calculator or circle calculator. The irregular-yard measuring guide explains partitions and measured-strip approximations.
Sources and method
- Math Is Fun: Area of Plane Shapes - trapezoid formula and perpendicular height.
- NIST: SI Units - Length - unit conversion factors.
Sources checked November 4, 2026. The examples and chart are calculations for this tool, not publisher estimates.