How to measure your beds
Measure the length and width of each bed in feet, then pick a depth in inches. For curved or irregular borders, draw the area as a few rectangles, calculate each one, and add the results together — a long, narrow border and a round island bed can be estimated this way without any geometry. Round generous: it is far better to have a little material left over than to stop a job halfway to reorder.
Enter the numbers above and the calculator returns cubic yards, the number of standard 2 ft³ bags, the cubic feet, and an estimated cost.
Depth guidance
The right depth depends on what you are spreading and why:
- Mulch (decorative or weed-suppressing): 2–3 inches. Less than 2 inches lets weeds through; more than 3 can smother shallow roots and hold too much moisture against stems.
- Topsoil for new beds or leveling: 4–6 inches so roots have room to establish.
- Compost worked into existing soil: 1–2 inches as a top dressing, or up to 3–4 inches when building a bed from scratch.
Refreshing old mulch? Measure only the new layer you plan to add, not the full bed depth, or you will badly over-order.
How the math works
Mulch, topsoil, and compost are sold by volume — usually the cubic yard in bulk. The calculator finds the volume of your bed and converts it to yards in one step:
- Cubic yards = (length × width × depth in inches) ÷ 324
The magic number 324 comes from combining two conversions: dividing depth by 12 to turn inches into feet, then dividing by 27 to turn cubic feet into cubic yards (12 × 27 = 324). Using it directly means you can go straight from square feet and an inch-depth to yards.
For small jobs the calculator also converts the volume into 2 ft³ bags, rounding up to whole bags since you cannot buy a partial one.
Bags vs bulk
Bagged material is convenient and easy to haul in a car, but it costs much more per cubic yard than a bulk pile. As a rough rule, once you pass about one cubic yard — roughly 13 to 14 of the 2 ft³ bags — bulk delivery is usually cheaper, even after a delivery fee. Bags still win for tiny touch-ups, hard-to-reach beds, or when you have no place to dump a pile.
A note on cost
The figure shown estimates material cost only, at national-average prices adjusted by region. Delivery, fuel surcharges, minimum loads, and labor are not included — use the regional adjustment and edit the unit price to match a local quote before you buy.