Material referenceMaterial guide

Mulch: categories, depth and coverage

Mulch is a category rather than a single product: bark, wood, and other organic materials are sold under the same word and behave differently. What they share is how they are planned — by volume, at a depth measured in inches — and that is what this page covers.

The categories you will actually see

Mulch products are usually grouped by what they are made from and how they are processed. The visible differences — colour, texture, particle size — come from those two things. The practical differences are how fast the material breaks down, how well it stays in place, and how it behaves around water.

Common mulch categories and their planning characteristics
Category	Typical form	Planning characteristics
Bark mulch	Shredded or chipped bark, often aged	Tends to knit together and stay in place; breakdown rate varies with particle size
Wood chip mulch	Chipped wood from a range of sources	Coarse and slower to break down; appearance varies widely between batches
Shredded or double-ground mulch	Finer texture, often with a uniform colour	Sits neatly and knits quickly; finer texture can hold more moisture against the soil
Composted or aged material	Further decomposed, darker	Closer to a soil amendment than a cover; behaves differently in wet conditions
Non-organic cover materials	Stone, rubber and similar	Planned like other aggregates; they do not break down, so they are replaced rather than topped up

No single category is best. The right choice depends on what is being planted, how the bed drains, how it looks from the house and how often you want to top it up.

Colour fades, structure does not

Dyed mulch can lose colour over a season while keeping its structure. If colour consistency matters, ask how the product is coloured and how it holds up, rather than judging from a fresh sample.

Depth: the number that matters most

Mulch depth is a narrow band, because both extremes cause problems. Too thin and it does not suppress weeds or hold moisture. Too thick and it holds water against stems and trunks, which is where many mulch-related plant problems begin.

Mulch: the planning depth ranges behind the calculator's presets
Use case	Planning range	Default	Note
Garden bed	2–4 in	3 in	Keep mulch off plant stems and trunks.
Tree ring	2–4 in	3 in	Do not pile against the trunk.

Planning ranges, not site-specific specifications. Your soil, drainage and use can justify a different depth.

Mulch out, not up

Penn State Extension puts the guidance simply: no deeper than the heel of your hand, generally 2–4 in, mulch less on poorly drained soil or with finely textured mulch, and keep all mulch away from the trunk so the root flare stays visible. This calculator uses the same range as its planning defaults.

Coverage and quantity planning

Mulch is planned like any other bulk material: area × depth ÷ 12 gives cubic feet, and ÷ 27 gives cubic yards. Because mulch is light, weight rarely matters; volume is what the supplier sells and what your bed consumes.

Coverage by depth, calculated with the engine's coverage function
Depth	One cubic yard covers	One 2 cu ft bag covers	One 3 cu ft bag covers
2 in	162 sq ft	12 sq ft	18 sq ft
3 in	108 sq ft	8 sq ft	12 sq ft
4 in	81 sq ft	6 sq ft	9 sq ft

Mulch settles after spreading, so the depth you buy and the depth you see a month later are different numbers. Plan the spread depth, not the settled one.

Mulch: planning assumptions used by the calculator
Assumption	Planning value
Typical density	0.35 tons/cu yd
Density range seen in practice	0.25–0.6 tons/cu yd
Bag sizes used for bag estimates	2 cu ft, 3 cu ft
Default waste allowance	10%
Order rounding	Nearest 0.25 cu yd

Fresh, wet mulch weighs far more than dry. Mulch is normally sold by volume.

Recalculated by the calculator engine as this page is built

Six tree rings at four feet diameter, three inches deep

Six circular tree rings, each 4 ft across, entered separately so the calculator adds them and the result shows the combined order. Depth is 3 in with the default 10% waste allowance.

Inputs

Material: Mulch
Area: 4 ft diameter + 4 ft diameter + 4 ft diameter + 4 ft diameter + 4 ft diameter + 4 ft diameter
Depth: 3 in
Waste: 10%

Project area: 75.4 sq ft7 m²
Depth used: 3 in
Volume before waste: 18.85 cu ft0.7 cu yd
Waste allowance: 10%
Volume to order: 20.73 cu ft0.77 cu yd · 0.59 m³
Order quantity: 1 cu ydRounded up to the nearest 0.25 cu yd
Estimated weight: 0.27 tons0.24 tonnes at the 0.35 tons/cu yd planning density
2 cu ft bags: 11 bags
3 cu ft bags: 7 bags
Bags or bulk?: Bags or bulk delivery are both reasonable

Same area at different depths (engine output, 10% waste)
Depth	Volume to order	Order quantity	Estimated weight	Smallest bag size
2 in	0.51 cu yd	0.75 cu yd	0.18 tons	7 bags
3 in	0.77 cu yd	1 cu yd	0.27 tons	11 bags
4 in	1.02 cu yd	1.25 cu yd	0.36 tons	14 bags

Every column comes from the same calculation engine used by the calculator.

This is the case where bags compete seriously: the combined area of a handful of tree rings is small enough that a bagged purchase is a reasonable choice, and the coverage table shows exactly how few square feet each bag covers. Remember to keep the mulch clear of the trunk, which means the area you actually cover is a ring rather than a full circle.

Bags versus bulk

A cubic yard is 27 cu ft, which is about nine 3 cu ft bags or thirteen and a half 2 cu ft bags. Comparing a bag price with a bulk price per cubic yard is the only fair comparison, and the calculator shows both counts for your own volume.

Bags are practical for a single tree ring, a repair, or a bed you are mulching one wheelbarrow at a time.
Bulk becomes practical once the volume passes roughly half a cubic yard, and it is usually cheaper per cubic foot.
Bulk arrives as a pile, so ask where it can be placed; a pile on a lawn you still have to mow is an irritation you will remember for a season.
Compressed or baled products expand after opening. Use the fill volume printed on the label, and check whether it refers to the compressed or the spread state.

Practical considerations

Mulch is normally sold by volume even when it is priced by weight, so keep the two units separate when comparing quotes.
Do not measure against a plant you are trying to keep dry: keep the layer clear of stems and pull it back from the base of shrubs and trees.
Fresh, wet mulch weighs far more than dry mulch, which matters if you are moving it by barrow and if a delivery has to sit on a driveway.
A bed that already has a mulch layer needs less than the calculation suggests unless you plan to rake the old layer out first.
Termites and other wood-dwelling insects are a common reason people choose a different material near a building. That is a site decision, not a universal rule about mulch.

Topping up is normal

Organic mulch settles and decomposes, so a bed that is topped up annually needs less material each time than the bed needed on the first application. Calculate the top-up depth, not the full depth, for an established bed.

Related guides

Keep going

How to calculate mulchMeasuring beds, bag comparisons and settling, step by step
Bagged versus bulk mulch pricingHow to compare bag and bulk quotes fairly
Topsoil, garden soil and compost comparedThe layer that may belong under the mulch
Open the Mulch Calculator

Try it: Mulch Calculator

Plan mulch coverage by depth, cubic yards and bags. Every number on this page came from the same engine, so you can replace the example figures with your own measurements and compare.

Frequently asked questions

Which mulch is best?

There is no universal answer, and any guide that gives one is simplifying. Coarse materials tend to last longer and stay in place; finer materials knit faster and look tidier. What suits a bed depends on the plants, the drainage, how the area looks from the house and how often you want to top it up.

How deep should mulch be around a tree?

The range used here is 2–4 in, with the material kept clear of the trunk. Penn State Extension’s phrasing is a good rule to remember: no deeper than the heel of your hand, and keep it away from the trunk so the root flare stays visible.

How many cubic feet are in a bag of mulch?

Bagged mulch is normally sold in 2 cu ft or 3 cu ft bags. A cubic yard is 27 cu ft, so that is about 13.5 bags of the smaller size or nine bags of the larger. The calculator converts your own volume into both bag counts.

Does mulch need to be removed before adding more?

Usually not, provided the existing layer is not already too deep and has not matted into a water-resistant crust. Raking the old layer to break the surface before topping up helps water move through it. If the layer has built up over years, removing some material is a better answer than adding more.

Why is mulch sold by the cubic yard rather than by weight?

Because weight varies enormously with moisture and material. A cubic yard of dry mulch and the same volume soaked after rain can differ substantially in weight, while the volume stays the same. Volume is the stable measure of what a bed consumes.

Sources and references

Penn State Extension — Mulching Landscape TreesIndependent guidance on mulch depth and on keeping mulch clear of the trunk.

These references support the general background on this page only. Product data, local requirements and site conditions take precedence over anything published here.

Method and limitations

Where this estimate stops being useful

This guide describes planning characteristics, not horticultural recommendations for a specific planting. It does not assess soil, drainage, plant health, insect or disease risk, and it cannot tell you which product is appropriate for your beds, your climate or your building. Mulch behaviour also varies between suppliers and between batches of the same product. Take planting-specific advice from a horticultural or landscape professional.

The methodology page documents how volume, waste, compaction and purchase quantities are produced, and the about page explains what this platform does and does not do.