How to measure your beds
For a simple rectangular bed, measure the length and width in feet and enter them directly. The calculator multiplies them together to get the square footage, then factors in depth to work out volume.
If a bed is irregular — it curves, has a bump-out, or wraps around a corner — split it into two or more rectangles you can measure separately. Work out the mulch needed for each piece (or add the square footage of each piece together first), then sum the results.
For a circular bed, such as a ring around a tree or a round island bed, use the formula for the area of a circle: Area = π × r², where r is the radius (half the diameter). A tree ring with a 6 ft diameter has a 3 ft radius, so its area is π × 3² ≈ 28.3 sq ft. Since this calculator asks for a length and a width, you can enter that square footage as the length and 1 as the width — length × width still equals the correct area.
The formula and a worked example
The math behind this calculator, in two steps:
Cubic feet = Length ft × Width ft × (Depth in ÷ 12)
Cubic yards = Cubic feet ÷ 27
Dividing by 27 converts cubic feet to cubic yards, since a cubic yard is 3 ft × 3 ft × 3 ft = 27 cubic feet — and mulch is almost always priced and delivered by the cubic yard, or sold in 2 or 3 cubic foot bags.
Worked example: a bed measuring 10 ft × 20 ft, spread 3 inches deep:
10 × 20 × (3 ÷ 12) = 50 cubic feet
50 ÷ 27 ≈ 1.85 cubic yards
50 ÷ 2 = 25 bags of 2 cu ft mulch
Add the standard 5% waste allowance and that order grows to about 52.5 cubic feet — roughly 1.94 cubic yards, or 27 bags — a small buffer that's usually cheaper than running short mid-project.
How deep should mulch be
The right depth depends on what you're mulching. These are common starting points used in landscaping, not fixed rules:
- Flower and garden beds: 2–3 inches is typically enough to suppress weeds and retain soil moisture.
- Around trees and shrubs: 3–4 inches is common, spread in a wide, flat ring well past the trunk.
- Refreshing existing mulch:if last year's mulch has broken down but isn't gone, a thin 1–2 inch top-up usually restores color and depth without over-mulching.
Avoid piling mulch up against tree trunks or plant stems in a cone shape — landscapers call this a "mulch volcano." It traps moisture against the bark, which can invite rot, disease, and pests, and it encourages roots to grow up into the mulch instead of down into the soil. Keep mulch a few inches back from any trunk or stem, tapering to a thin layer right at the base.
Bags vs bulk delivery
Bagged mulch is sold mainly in 2 cubic foot bags, with some brands offering 3 cubic foot bags. One cubic yard works out to 13.5 bags of 2 cu ft mulch, or 9 bags of 3 cu ft mulch.
| Depth | Coverage per cubic yard |
|---|---|
| 1 in | 324 sq ft |
| 2 in | 162 sq ft |
| 3 in | 108 sq ft |
| 4 in | 81 sq ft |
For small beds, bags are usually the more convenient choice and the per-yard cost isn't dramatically higher. Once a job needs more than about 2 cubic yards, bulk delivery is almost always cheaper and saves you from hauling and ripping open dozens of bags — as long as you have somewhere to dump and spread the pile.