How to Use This Calculator
Enter the length and width of your garden bed in feet. Set the depth in inches — 3 inches is the standard for bare soil, 2 inches for topdressing over existing mulch. The calculator returns cubic yards for bulk ordering, the equivalent number of 2 cu ft bags, and a cost range based on typical retail and bulk pricing. A 10% waste factor is included to account for settling, edges, and irregular borders. For beds with multiple distinct sections, run the calculator for each section and add the bag or cubic yard totals. If your bed is round or irregularly shaped, use our Square Footage Calculator to get your area first, then enter it here.
How to Calculate Mulch Coverage
The mulch formula starts with cubic feet: length (ft) × width (ft) × depth (in) ÷ 12. Dividing depth by 12 converts inches to feet so all three units match. Then divide cubic feet by 27 to get cubic yards, since one cubic yard is exactly 27 cubic feet.
Coverage reference by depth — how much area one cubic yard covers:
| Depth | Coverage per cubic yard | Bags (2 cu ft) per yd³ |
| 2 inches | 162 sq ft | 14 |
| 3 inches | 108 sq ft | 14 |
| 4 inches | 81 sq ft | 14 |
Worked example: a 25 × 8 foundation bed at 3 inches. Area = 200 sq ft. Cubic feet = 200 × (3 ÷ 12) = 50 cu ft. Cubic yards = 50 ÷ 27 = 1.85 yd³. With 10% waste: 1.85 × 1.1 = 2.04 — order 2.5 cubic yards or 28 bags of 2 cu ft.
Mulch Application Tips
Pull mulch back two to four inches from plant stems and tree trunks. Mulch piled against bark traps moisture against the cambium layer, causing rot and fungal disease. The mulch ring should be flat or slightly sloped away from the trunk, never mounded in the "volcano mulch" style commonly seen in commercial landscaping.
Apply mulch to moist soil, not dry soil. Water the bed thoroughly the day before mulching, or mulch immediately after rain. Mulch applied to dry soil locks moisture out instead of in. Once applied, mulch is most effective when it receives water within 24 hours so it can begin moderating the soil temperature beneath.
Refresh mulch every one to two years. Fine mulch like double-shredded hardwood breaks down faster than coarse bark chips. Before adding a fresh layer, rake the existing mulch to break up any matted, hydrophobic crust. A fresh top-dress of 1 to 2 inches restores appearance, weed suppression, and moisture retention without overcrowding roots.
What to Buy
For most garden beds, double-shredded hardwood mulch is the best all-purpose choice. It breaks down into organic matter that improves soil structure over time, stays in place on moderate slopes, and has a natural color that fades gracefully. Cedar mulch is worth the premium in areas with heavy pest pressure — the oils repel insects and resist fungal growth longer than hardwood.
For quantities up to 2 cubic yards, Scotts or Vigoro bagged mulch at major home improvement stores is convenient and consistent in quality. For larger projects, call local landscape suppliers and compare bulk pricing. Many suppliers deliver for free over a minimum order of 3 to 5 cubic yards. Bulk mulch is typically $25 to $45 per cubic yard versus $54 to $95 per yard-equivalent in bags.
Frequently Asked Questions
How much mulch do I need for a 10×10 garden bed? +
A 10 × 10 bed at 3 inches deep needs 0.93 cubic yards of mulch. With a 10% waste allowance, order 1 cubic yard or 14 bags of 2 cu ft mulch. If you prefer 2 inches of depth, the same bed needs 0.62 cubic yards — about 9 bags. Three inches is the standard for established beds; use 2 inches only for topdressing over existing mulch.
How deep should mulch be in a garden bed? +
Two to four inches is the correct range. Two inches is enough for topdressing beds that already have a layer underneath. Three inches is the standard for bare soil — it suppresses weeds, retains moisture, and moderates soil temperature effectively. Four inches is appropriate for slopes and areas with harsh sun exposure. Never go deeper than four inches; thick mulch suffocates roots and can harbor rodents.
How much does one cubic yard of mulch cover? +
One cubic yard covers exactly 108 square feet at 3 inches deep, 162 square feet at 2 inches deep, or 81 square feet at 4 inches deep. The formula is: coverage = 324 ÷ depth in inches. This is the most useful number to remember when buying mulch in bulk from a landscape supplier.
How many bags of mulch equal one cubic yard? +
One cubic yard equals 13.5 bags of 2 cu ft mulch (the most common bag size) or 9 bags of 3 cu ft mulch. Since you can't buy half a bag, plan on 14 bags of 2 cu ft or 10 bags of 3 cu ft per yard. Bulk mulch by the yard is almost always cheaper per cubic foot than bagged for quantities over 2 cubic yards.
What is the cheapest way to buy mulch? +
For quantities under 2 cubic yards, bagged mulch from a home improvement store is convenient and often price-competitive when sales are running. For anything over 2 cubic yards, bulk delivery from a landscape supplier is cheaper — typically $25 to $45 per cubic yard compared to $4 to $7 per 2 cu ft bag ($54 to $95 per cubic yard equivalent). Some municipalities give away free mulch from chipped tree removal debris — check your city's public works department.
How much mulch do I need for a 20×20 area? +
A 20 × 20 area is 400 square feet. At 3 inches deep, that needs 3.70 cubic yards of mulch. With 10% waste, order 4 cubic yards or 55 bags of 2 cu ft. At 2 inches deep the same area needs 2.47 cubic yards — about 3 yards or 37 bags. For a project this size, bulk delivery is almost always cheaper and less work than hauling individual bags.
Should I remove old mulch before adding new mulch? +
Only if the existing layer is 3 or more inches deep already. If it is, rake and loosen it first, then top-dress with 1 to 2 inches of fresh mulch. If the old mulch has matted and is repelling water — you can test this by dripping water on it and watching if it beads — rake it thoroughly to break up the hydrophobic crust before adding fresh material. Never just add layer on top of layer; deeply piled mulch smothers roots and creates rodent habitat.
How much mulch do I need for a long narrow flower bed? +
The shape doesn't change the math — enter your total square footage into the calculator regardless of shape. For an irregular or L-shaped bed, break it into rectangles, calculate each section, and add the results. A bed that is 40 feet long by 3 feet wide is 120 square feet. At 3 inches deep, that needs 1.11 cubic yards or 16 bags of 2 cu ft mulch.
