Mulch helps cover garden beds, retain soil moisture and create a tidy landscape. For most beds, you need enough to cover the soil about 2 to 3 inches deep. That works out to roughly one cubic yard, or 14 bags of 2 cubic feet, for every 110 to 160 square feet of bed.
The exact amount depends on two things: the area you want to cover and how deep you want the layer. Measure your beds, choose a depth that suits what you are growing, then use the mulch calculator to estimate your quantity. It works out cubic yards, the number of 2 or 3 cubic foot bags and, if you add a price, the cost.
How to Measure Your Garden Bed
Measure only the parts you are going to mulch. On a typical lot, that means beds, borders, tree rings and paths, not the lawn, so the total is often much smaller than the size of the yard. Measure inside any edging, where the mulch will actually sit.
Rectangular beds
Measure the length and width in feet and multiply them. A bed 12 ft long and 4 ft wide covers 12 × 4 = 48 square feet.
L-shaped and irregular beds
Divide the bed into smaller rectangles, work out each one and add them together. An L-shaped bed made of a 10 × 4 ft section and a 6 × 3 ft section covers 40 + 18 = 58 square feet. In the calculator, choose Length × width and add each rectangle as a separate area, and it adds them up for you.
For a long curving border, measure the length along the middle of the border, take the average of a few width measurements and multiply the two.
Circular beds and tree rings
For a round bed, the area is 3.14 × radius × radius, where the radius is half the distance across. A round bed 6 ft across has a radius of 3 ft, so it covers 3.14 × 3 × 3 = 28.3 square feet.
Around a tree, leave a few inches of bare soil next to the trunk. Work out the area of the whole circle, then subtract the bare circle in the middle: area = 3.14 × (outer radius² − inner radius²). Enter the result in the calculator’s Total area box, as it does not take circles directly. The calculator page has a worked tree ring example if you want to check your numbers.
Raised beds and slopes
Mulch only covers the soil surface, so the height of a raised bed makes no difference. Measure the inside length and width of each bed and add the areas together. On a slope, measure along the ground rather than across the top, because the surface you are covering is larger than it looks on a plan.
How Deep Should Mulch Be?
There is no single right depth. It depends on what you are mulching, the type of mulch, how much is already there and what you want the layer to do. For landscape beds, Illinois Extension recommends a settled layer of 2 to 3 inches, and Nebraska Extension suggests thinner layers for flowers and vegetables than for trees and shrubs.
| Area | Typical settled depth |
|---|---|
| Flower beds and established landscaping | 2 to 3 in |
| Trees and shrubs | 2 to 4 in |
| Vegetable and annual flower beds | 1 to 2 in |
| Paths and walkways | Often 3 to 4 in |
| Topping up an existing layer | Only enough to reach your target, often about 1 in |
New beds vs established beds
A new bed on bare soil needs the full depth. In an established bed, check how much mulch is left before you buy more. Push a trowel into the layer in a few places and measure it. If about 1 inch remains and you want 3, you only need to add 2 inches, so enter 2 inches in the calculator.
Weeds and moisture
A layer in the 2 to 3 inch range blocks light from many weed seeds and slows evaporation from the soil, so beds need less watering. It will not stop every weed. Perennial weeds that spread by roots or runners, such as Bermuda grass, can grow up through mulch, so dig them out before you spread it. Going deeper than needed does not give better weed control and can cause other problems.
Signs of too much mulch
Too much mulch, or mulch in the wrong place, can harm plants. Look out for:
- Mulch heaped up a tree trunk in a cone, sometimes called a mulch volcano. Wet mulch against bark softens it and invites decay and insects.
- A trunk that goes straight into the ground with no visible flare where it widens into the roots.
- Soil under the mulch that stays soggy for days after rain.
- Roots growing up into the mulch layer instead of the soil.
Keep mulch a few inches away from trunks and stems, and rake out excess before adding more.
How to Calculate How Much Mulch You Need
Mulch is sold by volume, so multiply the area by the depth. Area is usually in square feet and depth in inches, so convert the depth to feet first by dividing it by 12.
- Cubic feet = area in square feet × depth in inches ÷ 12
- Cubic yards = cubic feet ÷ 27, because a cubic yard is 3 ft × 3 ft × 3 ft
Worked example: a 10 × 10 ft bed at 3 inches deep
- Area: 10 ft × 10 ft = 100 square feet.
- Depth in feet: 3 in ÷ 12 = 0.25 ft.
- Volume: 100 × 0.25 = 25 cubic feet.
- Cubic yards: 25 ÷ 27 = 0.93 cubic yards.
The mulch calculator also has an optional 10% allowance for settling and waste, which is switched on when the page loads. With it, the 25 cubic feet becomes 27.5 cubic feet, or 1.02 cubic yards. How much mulch really settles depends on the material and the conditions, so treat the 10% as a sensible margin rather than an exact figure.
To skip the arithmetic, enter your own bed sizes in the mulch calculator. It handles feet, inches, yards and metres, and can add up several bed sections at once.
How Many Bags of Mulch Do You Need?
Divide the volume in cubic feet by the volume printed on the bag, then round up to a whole bag. Bag sizes vary, so check the label. Bags of 2 and 3 cubic feet are common.
One cubic yard is 27 cubic feet. That is 13.5 bags of 2 cubic feet, so you would buy 14, or exactly 9 bags of 3 cubic feet.
| Bed and depth | Volume | 2 cu ft bags | 3 cu ft bags |
|---|---|---|---|
| 50 sq ft at 3 in | 12.5 cu ft | 7 | 5 |
| 100 sq ft at 2 in | 16.7 cu ft | 9 | 6 |
| 100 sq ft at 3 in | 25 cu ft | 13 | 9 |
| 200 sq ft at 3 in | 50 cu ft | 25 | 17 |
Bag counts are rounded up and leave out the 10% allowance. The volume is the theoretical amount for a perfectly even layer. In a real bed you lose a little around plants and edges, so buying the next whole bag up is usually wiser than buying the exact figure. For other depths and bag sizes, see the mulch coverage and conversion chart.
Bulk Mulch vs Bagged Mulch
Both work well. The better choice depends on how much you need, how you will move it and what your local suppliers charge.
| Bagged mulch | Bulk mulch | |
|---|---|---|
| Suits | Small beds, top-ups and gardens without vehicle access | Larger jobs and several beds at once |
| Sold by | The bag, often 2 or 3 cu ft | The cubic yard |
| Getting it home | Carry it yourself or pay for store delivery | Usually delivered loose, often with a delivery charge |
| Handling | Easy to carry and stack, but leaves plastic bags | Needs space for the pile and a wheelbarrow to move it |
| Storage | Sealed bags keep until you need them | Best spread soon after delivery |
How to compare the cost
Get a price per bag and a delivered price per cubic yard, then compare like for like. Multiply the bag price by the number of bags you need, remembering that 14 bags of 2 cubic feet make about one cubic yard. Compare that with the bulk price plus delivery. Some suppliers have minimum orders, so ask about those too. Once you have a price, the calculator can estimate the total cost per bag or per cubic yard.
How much does a cubic yard of mulch weigh?
It varies a lot with the material and how wet it is. Ask your supplier for the weight per yard before you load a trailer or pickup, and check your vehicle’s payload limit. Several smaller loads or a delivery may be safer than one heavy trip.
Does Mulch Type Affect How Much You Need?
Not the volume. A 3 inch layer over 100 square feet needs 25 cubic feet of any mulch. What changes is how the layer behaves after you spread it.
- Wood chips are coarse and chunky, which suits paths and the ground under trees. The wood chip calculator works in the same way.
- Shredded bark knits together, so it stays in place better on gentle slopes. Finer shreds pack down more as they settle, so they may need topping up sooner. Try the bark calculator.
- Straw is light and fluffy and is often spread over vegetable beds for winter. It settles a lot, so it is usually laid thicker than the depth you want to end up with.
- Pine straw is sold in bales rather than by volume, so use the pine straw calculator to count bales.
Fine mulch does not need more volume to reach the same depth, but because it compacts more, keep the 10% allowance and check the depth again after a few weeks.
When Should You Replace or Top Up Mulch?
Organic mulch breaks down, gets kicked onto lawns and paths and washes away in heavy rain, so the layer thins over time. How fast depends on the material, the weather and how much the area is walked on, so no fixed schedule suits every garden. Check before you buy:
- Measure the depth in a few places with a trowel.
- Rake up any matted or moldy layer so water can soak through.
- Add only enough to reach your target depth, and use that extra depth in the calculator.
- If the old layer is still deep enough, loosen it and leave it rather than adding more.
Frequently Asked Questions
Should I remove old mulch before adding new mulch?
Not usually. If the old mulch is loose and not too deep, rake it over and add a thinner layer on top. Remove it if it has matted into a crust that sheds water, or if adding more would leave the layer much deeper than you want.
How do I mulch a steep slope?
Heavy rain can wash mulch off steep ground. Shredded mulch that knits together tends to stay put better than loose chips or nuggets. Measure the slope along the ground for an accurate area, and on very steep banks consider ground cover plants instead.
Plan Your Next Step
Measure each bed, decide on a depth for each area and check how much old mulch is left. Then work out the cubic yards, bags and cost in the mulch calculator, and compare a few local prices for bags and bulk before you order.
About the author
Haali is the creator of Place Calculator. With a BSc in Chemistry, Physics and Mathematics, an MBA in Marketing and a master’s degree in International Business and Sales Management, Haali combines science training with hands-on purchasing experience to build calculators that help people order the right amount of material. Haali’s articles on agriculture have been published by AG Morning Clips and Wikifarmer.