Square Foot Calculator Trapezoid
Calculate the square footage of a trapezoid. Enter the two parallel bases and height to get the area in square feet.
Trapezoid Area Calculator
Enter the two parallel sides (bases) and the perpendicular height.
Height is perpendicular to both bases.
Bases must be parallel.
How to Calculate Square Footage of a Trapezoid
A trapezoid (trapezium) has two parallel sides of different lengths. Trapezoidal shapes are common in yards, roofing sections, driveways that widen or narrow, and unusually shaped lots. The formula averages the two bases and multiplies by the height.
Trapezoid Area Formula
Base A and Base B are the two parallel sides. The height is the perpendicular distance between the two bases — not the slanted side length.
Step-by-Step Instructions
- Identify the two parallel sides (Base A and Base B). These are the sides that run in the same direction.
- Measure both bases in feet — the top and bottom parallel edges.
- Measure the height — the perpendicular distance between the two bases (not the slanted side).
- Add the bases together, divide by 2 (this gives the average width), then multiply by the height.
Worked Examples
A driveway is 14 ft wide at the street, 10 ft wide at the garage, and 25 ft long.
[(14 + 10) ÷ 2] × 25 = 12 × 25 = 300 square feet
A garden bed is 8 ft wide at one end, 4 ft at the other, and 12 ft deep.
[(8 + 4) ÷ 2] × 12 = 6 × 12 = 72 square feet
Common Uses
- Driveways that widen toward the street or taper toward the garage
- Irregularly shaped lot sections between property boundaries
- Roof sections and dormers with different widths at top and bottom
- Retaining walls — calculating face area for material estimates
- Window and door headers — trapezoidal trim pieces
Trapezoid vs. Rectangle
A rectangle is a special case of a trapezoid where both bases are equal. If Base A = Base B, the formula simplifies to just Base × Height, which is the standard rectangle formula.
Frequently Asked Questions
How do I calculate the area of a trapezoid? +
Add the two parallel bases together, divide by 2, then multiply by the perpendicular height: Area = [(Base A + Base B) ÷ 2] × Height.
What is the height of a trapezoid? +
The height is the perpendicular distance between the two parallel sides (bases). It is NOT the length of the slanted side.
What is a trapezoid? +
A trapezoid (trapezium in British English) is a 4-sided shape with exactly one pair of parallel sides. The parallel sides are called bases, the non-parallel sides are called legs.
Where do trapezoid shapes appear in real life? +
Driveways that widen at the street, tapered garden beds, roof dormers, window sills, and irregularly shaped lot sections often form trapezoids.
What is the area of a trapezoid with bases 14 and 10 ft and height 8 ft? +
Area = [(14 + 10) ÷ 2] × 8 = 12 × 8 = 96 square feet.