Reference

Bed shapes — circle, L, ring, trapezoid math

Updated May 2026 4 min read

Generic calculators stop at length × width. Real yards have curves, tree rings, and corners that wrap. Here's the math, with a diagram for each.

Rectangle

length × width

The default. Square beds, foundation borders, paver pads. Measure to the outside edge of the bed.

π × (diameter / 2)²

Round island beds, decorative gravel rings, planters. One number — the diameter — gives you the area.

½ × base × height

Corner beds, tucked-in plantings. The height is the perpendicular distance from base to opposite point — not the slanted edge.

(A × B) − (C × D)

Common for foundation borders that wrap a corner. Treat as a big rectangle with a smaller rectangle removed from one corner.

π × ((outer/2)² − (inner/2)²)

Mulch rings around trees. Subtract the trunk diameter from the outer ring diameter so you don't over-order.

½ × (A + B) × height

Wedge-shaped beds along a curved walkway or property line. A and B are the parallel sides; height is perpendicular between them.

The calculator handles all six. Pick the shape, plug in numbers, get bag count.