Mulch Calculator

13.5 bags at 2 cubic feet, or 9 bags at 3 cubic feet. A cubic yard is 27 cubic feet, so 27 divided by 2 is 13.5 and 27 divided by 3 is exactly 9. Since you cannot buy half a bag, a full cubic yard in 2 cu ft bags means buying 14 and having 1 cubic foot spare.

Read the bag before you multiply. Two and three cubic feet are the common sizes for bark and wood mulch, but some cedar and hardwood products come in 1.5 cu ft bags, and rubber mulch is usually sold by weight. The volume is printed on the front of the bag.

The usual working figures are 2 to 3 inches for an established flower or shrub bed, 3 to 4 inches around trees and shrubs and on paths, and only 1 to 2 inches on a new perennial bed or anywhere you have seedlings, because deep mulch smothers small plants and buries their crowns.

Two inches is roughly the minimum that blocks enough light to stop weed seeds germinating, which is why thinner mulch so often looks like it failed. Going much past four inches stops helping and starts holding water against stems and keeping the soil cold and airless in spring. If you already have mulch down, measure what is left and top up to the target rather than adding a fresh full depth every year.

Because bark is not root tissue and it is not built to stay wet. Mulch heaped against a trunk, the shape people call a mulch volcano, holds moisture against the bark, which invites rot and bark-boring insects, and it hides the root flare so the damage goes unnoticed for years.

Worse, the tree responds to the moist material around its trunk by growing new roots up into it. Those roots circle the trunk instead of spreading outward, and as both thicken they choke the tree's own plumbing. That is a girdling root, and it kills established trees slowly enough that nobody connects the cause to the mulch. Leave a few inches of bare soil all the way round, keep the ring flat and wide, and use the bare gap field in the circle mode above so you are not even buying that mulch.

Bags win when the job is small, when you have no driveway to dump a pile on, or when you want to spread it over several weekends. There is no minimum order, no delivery fee, and nothing sitting in the rain.

Bulk wins on volume. A cubic yard is 13.5 of the 2 cu ft bags or 9 of the 3 cu ft bags, and every one of those is a plastic sack to open, carry and dispose of. The crossover is usually somewhere around one to two cubic yards, but it is set by local pricing and delivery fees rather than by any rule, so call two suppliers and ask for their minimum load and their delivery charge before you decide. We will not quote a price here, because mulch pricing varies by region, by material and by season more than almost any other landscape material.

Measure the bed and use the same arithmetic as the calculator. A bed 6 ft long and 5 ft wide, filled to a level 1 ft deep, holds 30 cubic feet, which is 1.11 cubic yards. Fill the same bed 2 ft deep, to the top of the sides, and it is 60 cubic feet or 2.22 cubic yards.

Volume is not the limit, though. Weight is. Mulch is light compared with soil or gravel, but a wet load is much heavier than a dry one, and the number that matters is the payload rating on the sticker in your door jamb, not the size of the box. Ask the yard what a yard of the specific material weighs on their scale that day rather than trusting a general figure.

Use the circle mode. The area of a circle is pi times the radius squared, so a ring with a 6 ft outside diameter has a 3 ft radius and covers 28.27 sq ft. At 3 inches deep that is 28.27 x 0.25 = 7.07 cubic feet, which is 4 bags of 2 cu ft or 3 bags of 3 cu ft.

If you leave the bare gap at the trunk that you should, subtract it. With a 12 inch bare circle in the middle, the mulched area is pi divided by 4, times 6 squared minus 1 squared, which is 27.49 sq ft. The calculator does that for you when you fill in the gap field, and the difference is small, which is exactly the point: leaving the gap costs you almost nothing and it is the single most useful thing on this page.

Organic mulch breaks down, which is a feature rather than a fault, since that is how it feeds the soil. Most gardens end up topping up once a year, usually in spring, but the honest answer is to measure rather than to schedule.

Push a finger or a trowel into the bed and see how deep the remaining mulch is. If there are two inches left and you want three, you need one inch, not three, and one inch over 500 sq ft is 41.67 cubic feet instead of 125. That single check is where most of the overspending on mulch happens.

Usually not, and in a planted bed it often makes things worse over time. Mulch suppresses weeds by blocking light, and three inches of mulch does that on its own. Fabric stops the mulch from breaking down into the soil, so you lose the main long-term benefit of mulching.

What actually happens in a few seasons is that organic matter collects on top of the fabric, weeds root in that layer, and their roots grow through the mesh so they are harder to pull than they would have been. Fabric earns its place under gravel, under a path, or anywhere nothing is meant to grow and the covering is not meant to decompose. Under bark mulch in a flower bed, skip it.