Mulch Calculator

How to use the mulch calculator

Measure each bed’s length and width in feet at its longest and widest points. Garden beds are rarely tidy rectangles — for a curved or tapering bed, use the average width: measure the widest and narrowest spots and split the difference. For beds that wrap a corner or snake along a fence line, break the shape into two or three rough rectangles, run the calculator per section, and add the results. Precision to the inch is wasted effort here; mulch spreads and settles.

Depth is the setting that actually drives the number, and it’s where most people over- or under-buy. Three inches is the standard for weed suppression and moisture retention in shrub and perennial beds. Two inches is right for an annual top-up over last year’s layer, or around shallow-rooted annuals. Going past four inches buys you nothing — it suffocates roots, holds excess moisture against stems, and invites fungus.

Keep mulch pulled back two to three inches from trunks, stems, and your home’s siding. The cone of mulch piled against a tree — the "mulch volcano" — holds moisture against bark, rots it, and shelters rodents that chew it. Taper the layer down to nearly nothing at the trunk and put the full depth out at the drip line where the roots actually are.

The result reads two ways on purpose. Cubic yards is the bulk-order number — what a landscape supplier’s website and delivery driver both speak. The bag count is the same volume in store bags (2 cu ft standard; switch to 3 cu ft under Advanced for the bigger bags some stores carry). Compare total bag cost against bulk-plus-delivery: bulk usually wins somewhere around a cubic yard, but a delivery fee on a small order can flip the math back to bags.

For multiple beds, run the calculator once per bed and add the volumes — then order once. One combined bulk delivery beats three small ones on price every time, and leftover mulch keeps fine in a tarped pile for next season’s top-up.

The formula

Mulch is a volume calculation: area times depth, with inches converted to feet and cubic feet to the yards bulk yards are sold in:

cubic feet = length × width × (depth in inches ÷ 12)
cubic yards = cubic feet ÷ 27
bags = cubic feet ÷ bag size, rounded UP to a whole bag

Worked example with the defaults: a 12 × 4 ft bed at 3 inches deep is 12 × 4 × 0.25 = 12 cubic feet. Divide by 27 and that’s 0.44 cubic yards for a bulk order — or 12 ÷ 2 = 6 standard bags.

The handy conversion to memorize: one cubic yard equals 27 cubic feet, which is 13.5 standard 2 cu ft bags or 9 large 3 cu ft bags. A yard of mulch covers about 108 sq ft at 3 inches deep.

Frequently asked questions