Mulch is sold two ways, and they are not priced alike
Mulch comes bagged, usually 2 cubic feet a bag, or bulk by the cubic yard. A cubic yard is 27 cubic feet, so it takes 13.5 bags of the 2 cu ft size to make one — or 9 of the 3 cu ft size. That ratio is the whole reason this calculator reports both numbers: a bed that needs a yard and a half of mulch is either one small delivery or twenty bags to lift, open, empty and dispose of.
Because mulch is bought by volume and spread by depth, cost scales directly with how deep you lay it. Going from 2 inches to 4 doubles the order. That makes depth the single most consequential field on this page, and the one most often set too high.
Using this mulch calculator
Enter the bed's dimensions and the depth you want. The volume appears in cubic yards or cubic metres, alongside the bag count, the area covered, and the raw cubic feet.
The bag size selector switches between the two common retail sizes, so the bag count matches what is actually stacked at the store. Shape and units are in the customize panel: island beds are rarely rectangles, and a circle, trapezoid or rectangle border will usually fit the real bed far better than a bounding box would. For a ring around a tree, the circle border shape takes an outer and an inner diameter and subtracts the middle — which stops you paying for mulch you would never spread over the trunk.
The formula, worked through
Area in square feet times depth in feet, divided by 27 for cubic yards, then divided by the bag's volume for a bag count.
A 20 ft × 10 ft bed at 3 inches is 200 sq ft × 0.25 ft = 50 cubic feet — 1.85 cubic yards, or 25 bags of the 2 cu ft size. The same bed at 2 inches needs 33.3 cubic feet: 1.23 yards and 17 bags. That one-inch difference is eight bags, which is a useful thing to see before you buy rather than after.
A quicker version worth remembering: one cubic yard covers about 108 square feet at 3 inches deep, or 162 square feet at 2 inches. If a supplier quotes coverage rather than volume, that is the figure they are using.
How deep, and when to top up
Two to three inches is the working range. It is enough to block the light weed seeds need and to slow evaporation, without sealing the soil off from air and water. Deeper is not better: piling mulch against stems and trunks holds moisture where it causes rot, and a thick mat of fine mulch can shed rain rather than let it through.
Mulch also breaks down — that is the point of it, since it is feeding the soil as it goes — so beds settle by an inch or so a year. Topping up annually usually means ordering for the difference, not the full depth: measure what is actually there before you calculate, or you will buy roughly twice what the bed needs.
For a bed being built rather than refreshed, the topsoil calculator sizes the soil underneath, and the gravel calculator handles decorative stone where you would rather not re-mulch each year.
FAQ
How many bags of mulch are in a cubic yard?
A cubic yard is 27 cubic feet, so it comes down to the bag size:
| Bag size | Bags per cubic yard |
|---|---|
| 2 cu ft | 13.5 |
| 3 cu ft | 9 |
Stores don't sell half bags, so 13.5 means buying 14. This calculator always rounds up for you.
How deep should mulch be?
Two to four inches for most landscape beds, with two to three the usual sweet spot. That's enough to block light from weed seeds and slow evaporation, without holding so much moisture against the soil that roots are starved of oxygen. On poorly drained soils, use less.
Finely textured or double-shredded mulch packs tighter and lets less oxygen through, so use only 1–2 inches of it. And never pile mulch against a tree trunk — those cone-shaped “mulch volcanoes” trap moisture against the bark and rot it. Leave the flare at the base of the trunk exposed.
How much area does one cubic yard of mulch cover?
Coverage is just 27 cubic feet divided by your depth in feet:
| Depth | Coverage per cubic yard |
|---|---|
| 1 in | 324 sq ft |
| 2 in | 162 sq ft |
| 3 in | 108 sq ft |
| 4 in | 81 sq ft |
Is bulk mulch cheaper than bagged?
Almost always, once you need a full cubic yard. Fourteen 2-cu-ft bags typically cost noticeably more than one yard delivered loose, and that's before you've loaded, hauled, and split fourteen plastic sacks.
Bags win below about half a yard, when a delivery minimum or drop fee would swamp the saving, or when you have nowhere for a loose pile to sit. The rough break-even is around 7–10 bags.
What if my bed isn't a rectangle?
Open the customize panel (the sliders icon at the top right of the calculator) and pick the shape that matches: circle for a tree ring, circle border for a ring around a trunk, triangle or trapezoid for a corner bed. The diagram updates as you type, so you can check you've entered the dimensions the way it expects.
For genuinely irregular beds, break the shape into rectangles, run each through the calculator, and add the volumes together.
What else uses the same area-and-depth math?
Stone paths and gravel beds: our Gravel Calculator takes the same shapes and depth but also works out the weight, since gravel is sold by the ton.
Pouring a slab or path instead? The Concrete Calculator adds bag counts and a waste allowance.