Mulch is sold two different ways in two different units, and the cheaper option depends entirely on how much you need. This mulch calculator works in both, so you can see the bag count and the bulk volume for the same bed before deciding where to buy.
Three inches is the number that matters
Depth is not a matter of taste here. It is what determines whether the mulch does its job.
Below about two inches, enough light reaches the soil for weeds to germinate, which is most of the reason for laying mulch at all. Above four, it holds moisture against stems and crowns and starts causing the rot and pest problems it was meant to prevent. Three inches is the working target, and it is where this page starts. Penn State Extension puts the usable range at two to four inches and no more, and less than that where the soil drains poorly.
- A 20 by 10 foot bed at 2 inches takes 1.3 cubic yards, or 18 bags.
- The same bed at 3 inches takes 1.94 cubic yards, or 27 bags.
- At 4 inches it takes 2.59 cubic yards, or 35 bags.
Keep it off the trunks. Mulch piled against a stem or heaped around a tree base traps moisture where the bark needs air, invites rodents and rot, and kills established trees slowly enough that nobody connects the two. Pull it back a few inches from anything woody.
Where the bags-versus-bulk line sits
Bags at a garden center are measured in cubic feet, usually two per bag. A landscape supplier delivers in cubic yards, and a cubic yard is 27 cubic feet, so one bulk yard replaces about 13.5 bags, meaning 14 in practice.
Per cubic foot, bags typically run two to three times the bulk price. At $4.50 a bag, a cubic yard of mulch bought in bags costs around $63, against roughly $30 to $45 delivered. The crossover usually lands near two cubic yards, about 27 bags, where the saving finally outgrows the delivery fee.
What each option really costs you
- Bags need no tipping space, keep the driveway clean, and can be bought in stages. They also mean carrying, opening and disposing of every one.
- Bulk is cheaper per yard and faster to spread, but needs somewhere to dump a pile and the whole load moved before it is in the way.
- Delivery fees are the variable that decides it. Get the quoted fee before assuming bulk is cheaper on a small bed.
Refreshing rather than replacing
Organic mulch breaks down by roughly an inch a year, which is a feature rather than a fault: that is the material feeding the soil. An annual top-up of an inch or so maintains the depth, so measure what is already there and order the difference rather than the full three inches.
For the soil underneath a new bed, the topsoil calculator works out that layer, and the gravel calculator covers decorative stone if you are using an inorganic mulch instead.
Mulch calculator FAQ
About 13.5 bags at two cubic feet each, so 14 in practice, since a cubic yard is 27 cubic feet. At $4.50 a bag that is roughly $63 a yard against $30 to $45 for bulk delivery.
Three inches. Below two, enough light gets through for weeds to germinate. Above four, it holds moisture against stems and causes the rot it was meant to prevent. A 20 by 10 foot bed at 3 inches takes about 1.94 cubic yards.
Per cubic foot, yes, usually by two to three times. The crossover is around two cubic yards, about 27 bags, once the delivery fee is outweighed. Below that, bags often work out cheaper and need no tipping space.
About 1.94 cubic yards at the standard 3 inch depth, which is roughly 27 two-cubic-foot bags. At 2 inches it drops to 1.3 cubic yards, and at 4 inches it rises to 2.59.
Not usually. Organic mulch decomposes by about an inch a year and that breakdown feeds the soil. Measure the existing depth and top up the difference to three inches rather than laying a fresh full layer over it.