Mulch calculator: how many bags or yards for your beds
Two to four inches is the mulch depth the extension services recommend, and a 20 by 6 ft bed at 3 inches is 30 cubic feet. That is 15 bags of 2 cubic feet or 1.1 cubic yards in bulk, 17 bags once 10% is added for settling.
From bed area to bags
Each bed's area in square feet is multiplied by the depth in feet, giving cubic feet of mulch in place. Beds of any shape are added together, and a settling allowance is added because loose mulch packs down after the first rain. The total cubic feet divided by the bag size gives bags, rounded up to whole bags, and divided by 27 gives bulk cubic yards. When you type prices, bags are multiplied out and the bulk yards are priced with the delivery fee added once.
Cubic feet = area (sq ft) × depth (in) ÷ 12. Bags = cubic feet ÷ 2 (or ÷ 1.5 or ÷ 3 for the other sizes). Cubic yards = cubic feet ÷ 27.
Bags and yards for common bed sizes at 3 inches
| Bed | Area | Cubic feet | 2 cu ft bags | 3 cu ft bags | Bulk yards |
|---|---|---|---|---|---|
| Foundation bed, 25 × 4 ft | 100 sq ft | 25 | 13 | 9 | 0.93 |
| Island bed, 12 ft circle | 113 sq ft | 28 | 15 | 10 | 1.05 |
| Border, 40 × 6 ft | 240 sq ft | 60 | 30 | 20 | 2.22 |
| Ring around a tree, 8 ft across | 50 sq ft | 13 | 7 | 5 | 0.47 |
| Whole front yard, 500 sq ft | 500 sq ft | 125 | 63 | 42 | 4.63 |
Counts are before any settling allowance. At 2 inches, take two-thirds of each figure; at 4 inches, add a third.
A front yard with three beds and two trees
Two foundation beds of 20 by 4 ft are 160 square feet. An island bed 10 ft across is 78.5 square feet. Two tree rings 6 ft across, with the 4 inches nearest each trunk left bare, come to about 54 square feet. The beds get 3 inches and the rings 3 inches too, so the whole 292 square feet needs 73 cubic feet of mulch. With 10% for settling, that is 80 cubic feet. That is 41 bags of 2 cubic feet, 27 bags of 3 cubic feet, or 2.98 cubic yards in bulk. Forty-one bags fit in two trips with a car. The other choice is one delivery of 3 yards dumped on the driveway and moved with about 14 level loads of a 6 cubic foot barrow. Type the bag price and the yard price plus delivery to see which is cheaper where you live.
Depth and clearance, from the extension services
| Where | Depth | Clearance |
|---|---|---|
| Beds, annuals and perennials, composted or fine mulch | 2 to 3 in | an inch or two from stems |
| Shrubs and trees, coarse mulch | 3 to 4 in, out toward the drip line | 3 to 6 in from the trunk: Maryland 3, Illinois at least 4, Colorado 6 |
| Poorly drained soil | the low end of the range | same |
| Topping up last year's layer | enough to bring the total back to 2 to 4 in | rake the old layer first |
A pile of mulch against a trunk, the "volcano" shape, holds moisture against the bark and invites rot and pests. A flat ring with a bare center is what the extension services ask for; how deep mulch should be has each service's depth.
Measuring beds that are not rectangles
Walk the bed with a tape and break it into rectangles, circles and triangles. The shape options cover each, and a ring takes a tree bed with the trunk left out. Measure a curved border as a long rectangle using the average width, which is close enough for mulch. For a slope, measure along the ground rather than across the top. Add each bed as its own line, and the calculator keeps them separate in the list. So you can split the bags or the truck between the front and the back of the house.
Questions about buying mulch
How many bags of mulch are in a cubic yard?
A cubic yard is 27 cubic feet. That is 13.5 bags of 2 cubic feet, 18 bags of 1.5 cubic feet, or 9 bags of 3 cubic feet. So a bulk yard replaces about 14 of the common bags. The price of 14 bags is the number to compare with a yard delivered.
How much mulch do I need?
Multiply the bed area in square feet by the depth in feet (3 inches is 0.25 ft) for cubic feet. Then divide by 2 for bags or by 27 for yards. A 100 square foot bed at 3 inches is 25 cubic feet: 13 bags or just under a yard. The calculator adds the beds and the settling allowance for you.
How deep should mulch be?
Mulch goes on 2 to 4 inches deep, by the University of Illinois Extension and the Mulch and Soil Council. That is 2 to 3 inches for composted and fine mulch, 3 to 4 inches for coarse mulch, and less where the soil drains poorly. Keep it at least 4 inches away from tree trunks, and never pile it against stems. When you are topping up last year's layer, add only enough to bring the total back inside that range.
How much does a yard of mulch cover?
A cubic yard of mulch covers 162 square feet at 2 inches, 108 square feet at 3 inches and 81 at 4 inches. A single 2 cubic foot bag covers 12 square feet at 2 inches and 8 square feet at 3 inches.
Is it cheaper to buy mulch in bulk or in bags?
It depends on the delivery fee and the local prices, which is why the options take both. A bulk yard replaces 13.5 bags, so divide the delivered price of a yard by 13.5 and compare it with the bag price. Bags stay convenient for a bed or two and for carrying to the back of the house. A bulk pile saves the lifting when the count passes a few dozen bags.
How much does a yard of mulch weigh?
About 524 pounds per cubic yard for wood chips at normal moisture, using Cornell University's figure of 19.4 pounds per cubic foot. That makes a 2 cubic foot bag about 40 pounds. Bark nuggets run lighter and wet shredded mulch heavier, so the weight line is a guide for the truck, not a figure to buy by.
Should I remove old mulch before adding new?
Only if it is matted or diseased. Rake the old layer to break the crust, and pull it back from stems and trunks. Add only enough new mulch to bring the total depth back to 2 to 4 inches. That is what the 1 inch top-up preset is for. Removing sound mulch throws away the layer that is already feeding the soil.
6 source documents
- University of Illinois Extension, Proper Mulching Techniques (2 to 4 in depth, mulch at least 4 in from the trunk), revised March 2024. Read 2 November 2026.
- Mulch and Soil Council, Mulch Selection Guide, depth of application 2 to 4 in. Read 2 November 2026.
- University of Maryland Extension, Mulching Trees and Shrubs (1 to 3 in, 3 in from trunks). Read 2 November 2026.
- The Scotts Company, Scotts Nature Scapes Color Enhanced Mulch product pages, 2 cu ft and 1.5 cu ft bags. Read 2 November 2026.
- Cornell Waste Management Institute, Compostable Raw Materials, Table 6, bulk density of wood chips (19.4 lb per cu ft). Read 2 November 2026.
- Colorado State University Extension, Mulching Trees and Shrubs (keep mulch at least 6 inches from the trunk). Read 2 November 2026.