Quick answer
Multiply the bed area in square feet by the depth in inches and divide by 324 for cubic yards, since Clemson Extension notes one cubic yard covers 324 square feet an inch deep. At 3 inches, the middle of the 2 to 4 inches extension services recommend, 100 square feet takes 0.93 cubic yards, or 13 bags of 2 cubic feet. Keep mulch a few inches away from tree trunks and plant stems.
How deep to spread mulch
- University of Illinois Extension: 2 to 4 inches in well-drained sites; 2 to 3 inches of composted material, 3 to 4 inches of coarse mulch.
- Clemson Extension: no more than 2 to 3 inches of fine wood and bark mulch, which can suffocate roots if piled deeper; coarse pine bark nuggets up to 4 inches.
- Morton Arboretum: 3 to 4 inches of medium to coarse mulch around trees and shrubs, and only a couple of inches in perennial beds.
How much to buy
Bed area in square feet × depth in inches ÷ 324 = cubic yards. A cubic yard is 27 cubic feet, so it fills 13.5 bags of 2 cubic feet or 9 bags of 3 cubic feet.
| Bed area | 2 in deep | 3 in deep | 4 in deep | 2 cu ft bags at 3 in |
|---|---|---|---|---|
| 50 sq ft | 0.31 yd³ | 0.46 yd³ | 0.62 yd³ | 7 |
| 100 sq ft | 0.62 yd³ | 0.93 yd³ | 1.23 yd³ | 13 |
| 200 sq ft | 1.23 yd³ | 1.85 yd³ | 2.47 yd³ | 25 |
| 300 sq ft | 1.85 yd³ | 2.78 yd³ | 3.7 yd³ | 38 |
| 500 sq ft | 3.09 yd³ | 4.63 yd³ | 6.17 yd³ | 63 |
| 1,000 sq ft | 6.17 yd³ | 9.26 yd³ | 12.35 yd³ | 125 |
A 2 cubic foot bag covers 12 square feet at 2 inches, 8 at 3 inches and 6 at 4 inches. For a tree ring or an odd-shaped bed, the mulch calculator works it out, in yards or bags.
Keep it off trunks and walls
University of Illinois Extension calls overmulching and piling mulch against trunks and the root flare among the most common causes of tree decline, and says to keep mulch at least 4 inches from the trunk. The Morton Arboretum calls the cone of mulch piled up a trunk "volcano mulching" and advises leaving a donut hole around the trunk instead. Clemson Extension says to keep mulch 2 to 3 inches from the stems of woody plants and 6 to 12 inches from the walls of buildings, and to mulch a circle 3 to 4 feet across around a new tree.
Topping up
Mulch breaks down. Clemson Extension says wood chips are usually completely decomposed within 2 years, and pine needles and bark mulches typically last 2 to 4 years before more is needed. The Morton Arboretum says to check the depth every year and replenish as needed, and University of Illinois Extension says to wait until the old mulch has decomposed, raking it to break up matted layers in the meantime. So check the depth before buying more, and add only enough to bring it back to the recommended total. Mississippi State Extension notes that heavy mulching over several years can build up soil around plants, and suggests raking off old mulch after 3 years before adding a new layer.
Frequently asked questions
How much area does a yard of mulch cover?
324 square feet at 1 inch deep, according to Clemson Extension, so about 108 square feet at 3 inches and 81 at 4 inches.
How many bags of mulch are in a yard?
A cubic yard is 27 cubic feet: 13.5 bags of 2 cubic feet or 9 bags of 3 cubic feet.
How deep should mulch be?
Generally 2 to 4 inches. University of Illinois Extension recommends 2 to 3 inches of composted material and 3 to 4 inches of coarse mulch; Clemson keeps fine wood and bark mulch to 2 to 3 inches.
Should mulch touch the tree trunk?
No. University of Illinois Extension says to keep it at least 4 inches from the trunk, and calls mulch piled against trunks one of the most common causes of tree decline.
Calculators for this
Mulch
Enter bed size and depth to see how much mulch you need in cubic yards and how many 2 or 3 cu ft bags to buy, for square or round beds.
Topsoil
Find how much topsoil, garden soil or compost you need for lawns, beds and leveling, in cubic yards, tons and bags, at any depth.
Cubic Yard
Convert length, width and depth to cubic yards for dirt, gravel, mulch, sand or fill.
Published 2026-11-08. Sources: Clemson Cooperative Extension, HGIC 1604 Mulch; University of Illinois Extension, Proper Mulching Techniques; The Morton Arboretum, How to mulch trees and shrubs; Mississippi State University Extension, P2301 Mulches for the Landscape. See how we calculate.