Mulch Calculator

How to Use This Calculator

A mulch calculator tells you exactly how many cubic yards or bags of mulch to order for any garden bed, based on the bed dimensions and desired depth. Enter your bed's length and width in feet. For a depth, use 2 inches to refresh an existing bed with mulch already in place, 3 inches for a new bed from scratch, and 3 to 4 inches if weed suppression is the main goal. Results include 10% extra for spillage, irregular edges, and settling. For L-shaped or wraparound beds, break the area into two rectangles, run the calculator twice, and add the cubic yard totals. The 2 cu ft bag count matches the standard size sold at Home Depot, Lowe's, and most garden centers. If your bags say 1.5 cu ft, multiply the bag count by 1.33.

How to Calculate Mulch

The formula uses three steps. Convert depth from inches to feet by dividing by 12. Multiply length × width × depth in feet to get cubic feet. Divide by 27 to get cubic yards — there are exactly 27 cubic feet in one cubic yard.

Formula: cubic yards = (length × width × depth ÷ 12) ÷ 27

Worked example: a 20 × 15 bed at 3 inches deep. Area = 20 × 15 = 300 sq ft. Volume = 300 × (3 ÷ 12) = 75 cubic feet. Cubic yards = 75 ÷ 27 = 2.78. Add 10% waste: 3.05 rounds up to 4 cubic yards to order. In standard 2 cu ft bags: 75 × 1.1 ÷ 2 = 42 bags.

Coverage reference: one cubic yard at 2 inches covers 162 sq ft. At 3 inches it covers 108 sq ft. At 4 inches it covers 81 sq ft. Use these numbers to double-check your result or to quickly estimate without a calculator.

Mulch Tips

Never apply more than 4 inches around plants or trees. Beyond 4 inches the pile traps moisture against stems and trunks, which invites crown rot, fungal disease, and rodent activity. This is sometimes called volcano mulching because of the cone shape. It looks full and intentional, but it slowly kills the plant over several seasons.

Pull mulch back 2 to 3 inches from tree trunks and plant stems. Direct contact holds moisture against bark longer than it should and gradually breaks down the cambium layer. The gap looks sparse but prevents damage that compounds over years.

Do not mix fresh mulch into old mulch. Old material that has gone grey and compressed forms a hydrophobic crust that sheds water rather than letting it reach roots. Rake out the matted layer first, then apply fresh mulch on top. This is the single most overlooked step in spring mulching.

Hardwood mulch decomposes faster than cedar or cypress. That is good for soil organic matter, and bad for weed suppression. If you're mulching mostly to block weeds, use coarser cedar or pine bark at 3 inches. For flower beds where you want to build soil quality over time, shredded hardwood is the better call.

What to Buy

Garden beds and tree rings: double or triple-shredded hardwood bark. It knits together, resists wind displacement, decomposes to improve soil, and stays put on mild slopes. Available bagged at all home improvement stores and in bulk from landscape suppliers.

For weed suppression on slopes or around shrubs: cedar or cypress mulch. It breaks down more slowly than hardwood, holds position better on grades, and has a natural resistance to insects that hardwood does not.

Bulk vs. bags: if you need more than 2 cubic yards, bulk delivery almost always costs less. One cubic yard from a landscape supplier runs $25–50 delivered, versus $55–90 per cubic yard buying 2 cu ft bags at retail. The crossover point is roughly 2 yards — below that, bags are often more practical because you can use exactly what you need without leftover material.

Enter your supplier's per-yard price in the optional field above for an exact cost comparison between bulk and bags.

Frequently Asked Questions