Mulch Calculator

How to use this calculator

Measure the length and width of the bed you're mulching and decide how deep the layer should be. Enter those three numbers and you'll get the volume in cubic feet and cubic yards — how bulk mulch is delivered — plus the number of bags. Mulching several beds? Add a row for each and they're totaled together.

The bag size menu is optional and starts on bulk. Pick the size printed on your bag to get a bag count, or leave it on bulk if you’re ordering loose mulch. Most bagged mulch is 2 cubic feet, but some brands sell 1.5 or 3 cubic foot bags, and the difference changes your count considerably.

The formula, explained

Mulch is simpler than gravel or sand because it's sold by volume, not weight — so there's no density step. You just need volume:

Length (ft) × Width (ft) × (Depth in ÷ 12) = cubic feet
Cubic feet ÷ 27 = cubic yards

There's a shortcut worth memorising. Because 12 × 27 = 324, you can go straight from feet and inches to cubic yards in one step:

Length (ft) × Width (ft) × Depth (in) ÷ 324 = cubic yards

That's the number to keep in your head at the garden center. For bags, divide the cubic feet by the bag size instead — 50 cubic feet at 2 cu ft per bag is 25 bags.

Worked example: a 20 ft × 10 ft bed at 3 inches

1. Area: 20 × 10 = 200 square feet
2. Convert the depth: 3 ÷ 12 = 0.25 ft
3. Volume: 200 × 0.25 = 50 cubic feet
4. Cubic yards: 50 ÷ 27 = 1.85 cubic yards
5. Or with the shortcut: 20 × 10 × 3 ÷ 324 = 1.85 cubic yards
6. In bags: 50 ÷ 2 = 25 bags

Twenty-five bags is about a full car load and roughly $75–$150. At this size it's worth pricing a bulk delivery before you start hauling.

How deep should mulch be?

Two to four inches is the working range for almost everything. Under two inches and weeds push straight through; over four and you start suffocating the roots you're trying to protect.

Use	Depth	Why
Fine or shredded mulch	2–3 inches	Packs tighter, so less is needed
Coarse bark or nuggets	3–4 inches	Chunky pieces leave gaps light gets through
Weed suppression	3 inches minimum	Below this, weed seeds still germinate
Around trees & shrubs	2–4 inches	Keep 3–6 in clear of the trunk
Vegetable beds	1–2 inches	Light layer; it works into the soil
Playground surfacing	9–12 inches	Impact absorption, not weed control

Four inches is the ceiling for living beds. Piling deeper keeps water from reaching the soil, starves roots of oxygen, and creates a warm, damp layer that pests and fungus enjoy.

How much area does mulch cover?

The quickest way to sanity-check a quote or a pallet of bags:

Depth	1 cubic yard covers	One 2 cu ft bag covers
1 inch	324 sq ft	24 sq ft
2 inches	162 sq ft	12 sq ft
3 inches	108 sq ft	8 sq ft
4 inches	81 sq ft	6 sq ft

One cubic yard equals about 13.5 standard bags — useful when you're deciding between a delivery and a trunk full of bags.

How much mulch for common bed sizes

All at 3 inches deep, the most common depth.

Bed	Area	Cubic yards	2 cu ft bags
Small bed (4 × 8 ft)	32 sq ft	0.30	4
Border (3 × 20 ft)	60 sq ft	0.56	8
Bed (10 × 10 ft)	100 sq ft	0.93	13
Bed (10 × 20 ft)	200 sq ft	1.85	25
Large bed (20 × 20 ft)	400 sq ft	3.70	50
All front beds	500 sq ft	4.63	63
Whole front yard	1,000 sq ft	9.26	125

What depth costs you

Depth scales the whole order, so it's worth being deliberate. The same 200 sq ft bed needs:

Depth	Cubic yards	Bags
2 inches	1.23	17
3 inches	1.85	25
4 inches	2.47	34

Going from 3 to 4 inches is a third more mulch for no extra benefit in a typical bed.

Step by step: how to measure your beds

1. Measure each bed separately and add a row for each. Averaging several beds into one rectangle is where estimates drift.
2. Break curved beds into rectangles. Most borders are close enough to a long rectangle — measure the average width rather than the widest point.
3. For a circular tree ring, use π × radius². A 6 ft diameter ring is about 28 sq ft, so enter it as 6 × 4.7.
4. Subtract nothing for plants. The gaps around stems are small, and the offcuts even out. Don't try to deduct plant footprints.
5. Measure the existing mulch first. If you already have 2 inches down and you want 3, you only need 1 inch of new mulch — enter 1, not 3. This is the single biggest saving on this page.

Mulch for tree rings

Ring diameter	Area	Cubic yards @ 3 in	2 cu ft bags
3 ft	7 sq ft	0.07	1
4 ft	13 sq ft	0.12	2
5 ft	20 sq ft	0.18	3
6 ft	28 sq ft	0.26	4
8 ft	50 sq ft	0.47	7

Tree rings take far less than people expect — a 6 ft ring is about four bags. Our guide on how much mulch to put around a tree covers the trunk gap and why it matters.

Choosing the right mulch

The main trade-off is how long it lasts against how well it stays put and what it does to your soil. Organic mulches break down and feed the soil, which is a feature, not a fault — it just means topping up.

Type	Lasts	Best for
Shredded hardwood bark	1–2 years	General beds and slopes — the fibres knit together and stay put
Bark nuggets	2–3 years	Flat beds around shrubs; they float and wash on slopes
Cedar or cypress	2–3 years	High-visibility beds; slow to break down
Pine straw	about 1 year	Acid-loving plants, slopes; very light to handle
Arborist wood chips	2–3 years	Paths and tree rings; often free from tree crews
Compost	under 1 year	Vegetable beds — feeds soil, but can carry weed seeds
Rubber mulch	indefinite	Playgrounds only; adds nothing to soil

On any slope, choose shredded over nuggets. Nuggets float, and the first heavy rain will move them to the bottom of the bed.

What will it cost?

• Bulk mulch: roughly $30–$60 per cubic yard
• Delivery: $50–$100 locally
• Bagged mulch: roughly $3–$6 per 2 cu ft bag

Where bags stop making sense

Job	Bags	Bulk (incl. delivery)
400 sq ft @ 3 in (3.70 cu yd, 50 bags)	$150–$300	$161–$322
1,000 sq ft @ 3 in (9.26 cu yd, 125 bags)	$375–$750	$328–$656

The crossover sits around 3 cubic yards, or roughly 40 bags. Below that, bags usually win once you count delivery — and you can buy them as you go. Above it, bulk is cheaper, and it's dramatically less handling: one delivery instead of 125 bags in and out of a car, plus 125 plastic bags to dispose of.

Common mulching mistakes

• Volcano mulching. Piling mulch up against a trunk traps moisture against the bark, invites rot and pests, and encourages roots to grow into the mulch instead of the soil. Leave a 3–6 inch gap all round the trunk.
• Spreading it too thin. Under 2 inches doesn't block light, so weeds come straight through and you've bought yourself nothing.
• Spreading it too thick. Over 4 inches blocks water and air. Roots suffocate, and a thick fine mulch can even shed rain rather than absorb it.
• Piling mulch against the house. It bridges the gap between soil and siding, holding moisture against the structure and giving termites a covered route in. Keep it 6 inches clear of the foundation.
• Adding a fresh 3 inches every year. Old mulch doesn't vanish. Check what's there first, fluff it up, and top up only the difference.
• Landscape fabric under organic mulch. It stops the mulch breaking down into the soil, which is half the point — and weeds root in the mulch on top of it anyway.

Pro tips for a bed that looks professional

• Edge the bed first. A clean cut edge, 2–3 inches deep, is what makes a mulched bed look finished, and it keeps the mulch where you put it.
• Weed and water before you mulch. Mulch locks in whatever moisture is there, so laying it over dry soil keeps the soil dry.
• Fluff before you buy. Existing mulch often mats into a crust. Raking it loose restores much of the look and depth for free.
• Refresh an inch a year, not three. Topping up the difference costs a third as much and avoids building a suffocating layer.
• Mulch in mid-spring. Wait for the soil to warm; mulching too early insulates cold soil and slows everything down.
• Ask a local tree service for chips. They often drop a free load. It's coarse, so it's ideal for paths and tree rings rather than display beds.

A note on accuracy

This calculator gives you a clean volume figure from your measurements. Bagged mulch is usually a little fluffier than the settled figure on the bag, and bulk mulch compresses in the pile, so treat the result as a close planning number and round up. Bulk suppliers often have a minimum delivery, so it's worth a quick call before you book.

Where these figures come from

The mulch depth guidance built into this calculator comes from the published sources below. The arithmetic itself — converting measurements to volume, and volume to bags or tons — is straightforward unit conversion, and you can check it in the full working the calculator shows. Material densities and bag yields vary by product and supplier, so confirm the figure printed on the bag or quoted by your yard before you order.

• Mulching Trees and Shrubs Source: University of Maryland Extension. Choosing mulch, the right depth, and keeping it off stems and trunks.
• Mulching Woody Ornamentals With Organic Materials (EC 1629) Source: Oregon State University Extension. A peer-reviewed publication on mulch materials and application depth.
• Mulches for Home Grounds (Fact Sheet 7.214) Source: Colorado State University Extension. Mulch materials and recommended application depths.
• Mulching for Soil and Garden Health Source: University of Minnesota Extension. Organic versus inorganic mulch and how mulch affects soil.

Frequently asked questions

How much mulch do I need for a 10x20 flower bed?

A 10 ft by 20 ft bed at 3 inches deep needs 50 cubic feet — about 1.85 cubic yards, or 25 bags at 2 cu ft each. At 2 inches it drops to 1.23 cubic yards (17 bags); at 4 inches it rises to 2.47 cubic yards (34 bags).

How many bags of mulch are in a cubic yard?

About 13.5 bags at the standard 2 cubic feet per bag, since a cubic yard is 27 cubic feet. If your bags are 1.5 cu ft it's 18 bags per yard, and at 3 cu ft it's 9. Always check the bag — sizes vary by brand.

How deep should mulch be?

Two to four inches for almost everything. Use 2–3 inches for fine or shredded mulch and 3–4 inches for coarse bark or nuggets. Three inches is the practical minimum for weed suppression, and four inches is the ceiling — deeper starves roots of water and oxygen.

How much area does a cubic yard of mulch cover?

One cubic yard covers about 162 sq ft at 2 inches deep, 108 sq ft at 3 inches, or 81 sq ft at 4 inches. A single 2 cu ft bag covers roughly 12, 8, or 6 sq ft at those same depths.

Should I buy mulch in bags or in bulk?

The crossover is around 3 cubic yards, or roughly 40 bags. Below that, bags usually work out similar once delivery is counted, and you can buy as you go. Above it, bulk is cheaper and far less handling — one delivery instead of dozens of bags to haul, open, and throw away.

How much mulch do I need around a tree?

Less than most people expect. A 4 ft diameter ring at 3 inches deep needs only about 0.12 cubic yards — roughly 2 bags. A 6 ft ring needs about 0.26 cubic yards, or 4 bags. Keep the mulch 3–6 inches clear of the trunk rather than piling it against the bark.

Do I need to remove old mulch before adding new?

Usually not. Rake the existing layer to break up any crust, measure what's left, and top up only the difference to reach your target depth. If the old layer is already 3–4 inches and matted, remove some before adding more — otherwise you build a layer deep enough to suffocate roots.

How much does mulch cost?

Bulk mulch runs roughly $30–$60 per cubic yard plus $50–$100 delivery. Bagged mulch is about $3–$6 per 2 cu ft bag, which works out to roughly $40–$80 per cubic yard before you count your time hauling it. Prices vary by region and mulch type.