Mulch coverage chart: how far a yard or a bag goes, and how deep to spread it

Mulch coverage chart

Coverage is simple geometry: a cubic yard is 27 cubic feet (a box 3 ft on each side), and spreading it 1 in deep covers 27 × 12 = 324 sq ft. Every extra inch of depth divides that by one more. The same works for bags, using the cubic feet printed on the bag.

Turned around, the chart gives the bag count: at 3 in, a 2 cu ft bag covers 8 sq ft, so a 100 sq ft bed needs 100 ÷ 8 = 12.5, call it 13 bags. That exact case, with the 2 in and 4 in versions, is worked out on How much mulch for a 10×10 area. A cubic yard is 13.5 bags of 2 cu ft or 9 bags of 3 cu ft — the bags in a cubic yard page covers every bag size.

Pick the depth on purpose

Depth drives the order more than anything else. Going from 2 in to 4 in doubles the mulch, so it is worth deciding rather than eyeballing. Penn State Extension recommends a 2- to 4-inch layer of organic mulch "and no more", with less on poorly drained soil, and the University of Minnesota Extension gives the same 2–4 in range as the balance between weed suppression and letting air reach the soil. Within that range:

More is not better past about 4 in. A thick blanket can keep soil soggy in wet climates, shed light rain before it reaches the soil, and encourage roots to grow up into the mulch instead of down. Mulch piled against stems and trunks holds moisture against bark; Penn State’s guide says to keep it 3–5 in away from young trees and 8–10 in from mature ones. The "volcano" of mulch you see around some commercial trees is exactly what arborists advise against — a 6 ft ring done properly is only about 4 bags, as How much mulch for a 6 ft tree ring shows.

Check what is already there

Most beds are not bare. Before buying, push a trowel through the old mulch in a few spots. If an inch or two remains, you only need enough to bring the total back to your target, which can cut the order in half. Penn State makes the point directly: new mulch spread over old in successive years is the same as applying too deep a layer at once. Old mulch that has matted into a crust can be broken up with a rake so water gets through, and then topped up.

Measure the beds

You don’t need precision; you need a sensible total. Three ways to get there:

• Rectangles. Most beds are close enough to one or two rectangles. Measure the longest length and the average width. A long foundation bed that is 3 ft wide at one end and 5 ft at the other averages 4 ft. The classic strip along a house is on How much mulch for a 3×40 ft foundation bed.
• Circles. Tree rings and island beds: measure across the middle (the diameter). The area is 3.14 × (diameter ÷ 2)². A 6 ft ring is about 28 sq ft; an 8 ft ring about 50.
• Pacing. An average adult stride is roughly 2.5 ft. Pace the length and width, and you will usually be within 10–15%, which is fine for mulch.

Add the areas together. If your beds total, say, 380 sq ft, round to 400 and move on. The beds around a typical house often come to something like How much mulch for 500 sq ft — about four and a half cubic yards at 3 in.

Turning area and depth into yards and bags

Mulch is sold by volume. Multiply the area in square feet by the depth in feet (inches ÷ 12) to get cubic feet. Divide by 27 for cubic yards, or by the bag size for bags. Bags are usually 2 cu ft, sometimes 1.5 or 3 cu ft.

cubic feet = area (sq ft) × depth (in) ÷ 12
cubic yards = cubic feet ÷ 27
bags = cubic feet ÷ bag size

In metric, 10 m² at 7.5 cm is 750 L — fifteen 50 L bags, or three-quarters of a cubic metre in bulk; see How much mulch for 10 m². For big landscapes, How much mulch for 1,000 sq ft runs to over nine cubic yards, which is a bulk-delivery job.

Which mulch?

For depth planning, the main difference between mulches is how much they settle and how fast they break down.

• Shredded hardwood knits together and stays on slopes. It breaks down at a moderate pace and feeds the soil as it goes.
• Pine bark nuggets last longer but float and wash away in heavy rain. Poor choice on slopes or near drains.
• Arborist wood chips are a mix of wood, bark and leaves. Some tree services give them away. Good for paths and around trees; let very fresh chips sit a few weeks if you are worried about appearance.
• Pine straw is light and covers a lot of ground per bale, but settles heavily. It is sold by the bale, not the yard — the pine straw calculator works in bales.
• Shredded leaves and straw work well in vegetable gardens and are cheap or free. Use straw, not hay, which is full of seeds.
• Stone and rubber don’t break down or feed the soil. Use the river rock calculator for stone; rubber mulch is mostly used under play equipment, where the CPSC playground handbook sets the depth by fall height.

A worked example

Suppose you have a 40 × 3 ft bed along the front of the house, two 6 ft tree rings, and a 12 × 8 ft island bed, all with about an inch of old mulch left. The areas are 120 + 28 + 28 + 96 = 272 sq ft. Topping up with 2 in gives 272 × 2 ÷ 12 = 45 cubic feet, or about 1.7 cubic yards. In bags that is 23 of the 2 cu ft size.

If the beds were bare and you wanted a full 3 in, it would be 68 cubic feet — about 2.5 yards, or 34 bags. That difference is why checking the old layer first is worth two minutes.

When to mulch

Spring, after the soil has warmed a little, is the most common time; mulch applied to cold soil keeps it cold longer. Late fall mulching after the ground cools helps protect perennials over winter. Either way, pull weeds first; mulch smothers seedlings, not established perennial weeds.

Common mistakes

• Adding a full new layer every year on top of the old one. Over a few seasons the total creeps past 6 in.
• Mulching right up against the house siding or over the top of the foundation. Leave a gap and keep the grade sloping away.
• Using landscape fabric under wood mulch. The mulch breaks down into soil on top of the fabric and weeds root into it anyway.
• Buying bulk without a place to put the pile. A driveway tarp and a plan for rain on the pile save cleanup.
• Skipping the edge. Without a cut edge or edging strip, mulch washes onto the lawn and grass creeps into the bed; the landscape edging calculator works out the feet and pieces.

If you are weighing a bulk delivery against a stack of bags, see bagged vs bulk mulch for how to find the break-even point with your own prices.