How much mulch for a 4 × 12 ft garden bed, 3 inches deep?
A 4 × 12 ft garden bed covers 48 sq ft. At 3 inches deep that is 0.44 yd³ of shredded hardwood mulch, so order 0.44 yd³.
Mulch to order
0.44 yd³
0.44 yd³ for the area, plus 0% extra. About 0.12 tons.
Mulch to order. 0.44 yd³. 0.44 yd³ for the area, plus 0% extra. About 0.12 tons.
| Cubic yards | 0.44 |
|---|---|
| Cubic feet | 12 |
| Weight | 0.12 tons |
| Bags of 2 cu ft | 6 |
| Bags of 3 cu ft | 4 |
| Area covered | 48 sq ft |
Weight uses 20 lb per cubic foot for this material, loose and dry. Wet material weighs more, so check with your supplier.
What this project needs
Penn State recommends a 2 to 4 inch layer of organic mulch and no more, and less on poorly drained soil. Keep it a few inches back from stems and trunks so they stay dry.
From bags, that is 6 bags of 2 cu ft. At this size bags are practical: there is no delivery fee or minimum order, and you can spread it as you go.
At 2 inches instead of 3, the same area needs 0.3 yd³, 33% less.
How it's calculated
The volume is the area times the depth: length × width for a rectangle, or π × radius² for a circle, times the depth in feet. 27 cubic feet make a cubic yard, and a foot is exactly 0.3048 m.
The extra covers settling and compaction. Loose stone and sand settle about 10%, road base compacts by about a third (Penn State: 8 in loose makes 6 in), and loose topsoil settles 20% to 30%. Mulch and compost are spread loose, so they start at no extra.
Weight is the order volume times the material's loose density: 100 lb per cubic foot for crushed stone, pea gravel and river rock, 111 for road base, 97 for sand, 78 for topsoil, 37 for compost and about 20 for mulch. Wet material weighs more.
Bags are rounded up to whole bags: gravel and sand come in 0.5 cu ft bags of about 50 lb, mulch in 2 and 3 cu ft bags, topsoil and compost in 0.75 and 1 cu ft bags.
The material cost uses the prices you enter: bulk stone, sand and road base are priced by the ton, mulch, topsoil and compost by the cubic yard. There are no built-in prices because they vary too much by area.
Sources
- Caterpillar Performance Handbook, Edition 50: Weight of Materials (loose density), Caterpillar Inc. (June 2022)
- Dirt and Mud Densities (gravel 105, sand 97, loam 80 lb/ft³), The Engineering ToolBox (2026)
- QUIKRETE All-Purpose Gravel No. 1151: 50 lb bag, 0.5 ft³, Quikrete International (product listing) (2026)
- Driving Surface Aggregate handbook: 8 in loose compacts to 6 in, 6 in to 4½ in, Penn State Center for Dirt and Gravel Roads (March 2025)
- Gravel Roads Construction and Maintenance Guide (compaction: 30% or more less volume), U.S. Federal Highway Administration (2015 (FHWA-OTS-15-0002))
- Tech Spec 2: Construction of Interlocking Concrete Pavements (base thickness), Interlocking Concrete Pavement Institute (February 2020)
- Public Playground Safety Handbook, Table 2: loose-fill surfacing depths, U.S. Consumer Product Safety Commission (July 2025)
- On-Farm Composting Handbook, Table A.1 (wood chips 445 to 620 lb/yd³), Cornell Waste Management Institute (NRAES-54)
- Mulching Landscape Trees: a 2 to 4 inch layer, Penn State Extension (April 2018)
- Mulch: 3 inches deep; one cubic yard covers 108 square feet, University of Florida IFAS Gardening Solutions (2026)
- Lawn Establishment: 4 to 6 inches (settled) of topsoil, Penn State Extension (September 2025)
- Creating Raised Bed Planters: 6 to 12 inches of soil, Iowa State University Extension (March 2024)
- EM 9217 Interpreting Compost Analyses (about 1,000 lb per cubic yard), Oregon State University Extension (2023)
- Using Composts to Improve Turf Performance: a ¼ inch top dressing, Penn State Extension (2026)
- NIST Handbook 44, Appendix C: General Tables of Units of Measurement, National Institute of Standards and Technology (2026)
Last reviewed October 2026.