Trapezoid Square Footage Calculator
Enter your measurements below to get the area of a trapezoid in square feet, square metres, square yards and acres. The live preview draws the trapezoid to scale as you type, labelled on a measured grid, and you can drag its handles to change the measurements.
Area = ((Base 1 + Base 2) ÷ 2) × Height
Live scale preview
The shape is drawn to scale and relabelled as you type.
An example to start from. Drag a handle or type a measurement and it becomes yours.
Worked example
A trapezoid with base 1 10 ft, base 2 14 ft, height 8 ft works out at 96 square feet.
| Unit | Area |
|---|---|
| sq ft | 96 |
| m² | 8.92 |
| sq yd | 10.67 |
| sq in | 13,824 |
| acres | 0.002204 |
When to use the trapezoid calculator
A trapezoid is a four-sided shape with exactly one pair of parallel sides. In a house they show up as bay windows, gable ends when you are ordering siding, angled kitchen extensions, driveways that widen towards the road, and plots that taper along a curved street.
The formula averages the two parallel sides and multiplies by the distance between them: ((14 + 10) ÷ 2) × 8 = 96 square feet for a patio with parallel sides of 14 ft and 10 ft standing 8 ft apart. The two non-parallel sides never enter the calculation.
Finding the parallel pair
Measure the gap between one pair of opposite sides at each end. If the two readings match, those sides are parallel and they are the ones to enter. If neither pair matches, the shape is a general quadrilateral and no trapezoid formula applies to it — split it along a diagonal into two triangles and add them, using the three-sides triangle calculator for each half.
Height, not the sloping side
As with a triangle, the height is the perpendicular distance between the two parallel sides, not the length of a slanted edge. Measuring along the slope always overstates the area. Where the slope is gentle the error is small, but on a steeply raked bay or gable it becomes significant quickly.
For an attic room, note that the trapezoid is the cross-section of the space, not the floor. Order flooring against the rectangular floor area and paint against the trapezoidal wall face — they are two different numbers for the same room.
Frequently asked questions
How do I calculate the square footage of a trapezoid?
Average the two parallel sides, then multiply by the perpendicular distance between them. A patio with parallel sides of 14 ft and 10 ft, 8 ft apart, is ((14 + 10) ÷ 2) × 8 = 96 square feet. The two non-parallel sides do not enter the calculation at all.
Which sides are the parallel ones?
The two that never meet, however far you extend them. In a room this is usually the pair of opposite walls that stay the same distance apart along their whole length — measure the gap between them at each end, and if the two readings match, those are your parallel sides. If neither pair matches, the shape is a general quadrilateral, and you should split it into two triangles instead.
Where do trapezoid areas come up in a house?
Bay windows, angled kitchen extensions, driveways that widen towards the road, and gable ends when you are calculating siding are all trapezoids. Attic rooms with a sloping ceiling are trapezoids in cross-section, though the floor beneath them is usually a plain rectangle — measure the floor for flooring and the wall face for paint.
Other shapes
A space that is not a trapezoid can nearly always be split into two or three of these and added together.
- Circle calculator
- L-Shaped Room calculator
- Parallelogram calculator
- Rectangle calculator
- Circle Sector calculator
- Square calculator
- Triangle calculator
- Triangle (Three Sides) calculator
To add several spaces into one figure, use the multi-room square footage calculator. To turn this area into an order quantity, see the material calculators.
New to the math? The square footage formula for every shape explains the calculation behind each of these tools.