How Much Mulch Do I Need? Coverage Charts, Depths and Bag Counts

Most people buy mulch twice: once by guesswork, then again when the first load runs out halfway along the border. The maths is simple once you know one number: a cubic yard of mulch covers about 108 square feet at 3 inches deep. Everything else follows from your area and the depth you choose, and depth is where most gardens go wrong.

This guide gives coverage charts, bag counts and depth recommendations from university extension services. For an exact figure for your beds, use our mulch calculator.

The quick formula

Cubic feet of mulch = area (sq ft) × depth (inches) ÷ 12

Cubic yards = cubic feet ÷ 27

A 10 × 20 ft bed (200 sq ft) at 3 inches needs 200 × 3 ÷ 12 = 50 cubic feet, which is 1.85 cubic yards, or 25 bags of 2 cubic feet.

How far a cubic yard goes

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

There are 27 cubic feet in a cubic yard, so it takes 13.5 bags of 2 cubic feet, or 18 bags of 1.5 cubic feet, to equal one yard. In metric, 1 cubic metre covers 13.3 m² at 7.5 cm deep, and a 50-litre bag covers about 0.67 m² at that depth.

How deep should mulch be?

University of Illinois Extension recommends 2 to 4 inches overall: about 2–3 inches for fine, compost-based mulches and 3–4 inches for coarse wood chips and bark. Thinner than 2 inches lets weeds through and dries out quickly; deeper than 4 inches starts to cause problems.

Why too much mulch hurts plants

Deep layers mat down and block water and oxygen from reaching roots, hold excess moisture against stems and bark, encourage decay and root rot, and give voles and mice a place to hide while they chew bark. Each year’s top-up adds to last year’s, so mulch quietly gets deeper over time.

Avoid the mulch volcano

Mulch piled up against tree trunks, sometimes called a mulch volcano, keeps the bark constantly wet and invites rot and girdling roots. Extension guidance is to keep mulch at least 4 inches away from the trunk and spread it in a wide, flat ring, ideally out toward the dripline, rather than a deep mound.

Which mulch should you buy?

• Shredded bark and wood chips: long-lasting, good for shrub and tree beds; apply 3–4 inches.
• Compost or leaf mould: feeds the soil and suits vegetable and flower beds; apply 2–3 inches and top up yearly.
• Straw: lightweight and ideal for vegetable rows and strawberries; use weed-seed-free straw.
• Gravel or stone: permanent, for dry gardens and paths; 2 inches is usually enough.

If you are improving the soil underneath at the same time, see how much compost you need with the compost calculator.

Bags or bulk?

Bags are easier for small beds and tidy to handle. Above roughly 2–3 cubic yards, bulk delivery is usually cheaper per yard, but you need a place for it to be tipped and a wheelbarrow to move it. Price both options using the bag and yard figures from the calculator.

How to measure your beds quickly

1. Break irregular beds into rectangles, circles and triangles and add them up. Our garden area calculator does this for odd shapes.
2. Subtract areas already covered by large shrubs or stepping stones.
3. Decide the depth by mulch type, then convert to yards or bags.
4. Add about 5–10% for uneven ground and settling.

Frequently asked questions

How many bags of mulch are in a yard?

About 13.5 bags of 2 cubic feet, or 18 bags of 1.5 cubic feet, make one cubic yard.

How much area does a bag of mulch cover?

A 2 cubic foot bag covers about 12 square feet at 2 inches deep or 8 square feet at 3 inches deep.

How much mulch do I need for 100 square feet?

At 3 inches deep you need 25 cubic feet: about 0.93 cubic yards, or 13 bags of 2 cubic feet.

Should I remove old mulch before adding new?

Not usually. Rake it to loosen it, check the total depth stays within 2–4 inches, and only top up the difference. Remove it if it is matted, mouldy or piled against stems.

When is the best time to mulch?

Late spring, once the soil has warmed, and again in autumn to protect roots over winter. Mulch after watering or rain, onto moist soil.

Sources: University of Illinois Extension, “Proper Mulching Techniques”; University of Vermont Extension, “Beware the Mulch Volcano”. Coverage figures are standard volume conversions.