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Generator Hut

Mulch Calculator

How much mulch a bed needs, in cubic yards or bags.

Your measurements

2–3 in suppresses weeds. Deeper than 4 in can starve roots of air.

Bagged mulch is usually sold in 2 cu ft bags.

Mulch required

1.48cu yd

1.48 cubic yards — or 20 bags

Bed area20 ft × 8 ft
160 sq ft
Volume requiredat 3 in deep
40 cu ft
In cubic yardshow bulk mulch is delivered
1.48 cu yd
Bags of mulch
20 × 2 cu ft

Bulk delivery beats bags on price somewhere around two cubic yards — that is roughly 27 two-cubic-foot bags, and the saving grows steeply from there.

Keep mulch clear of trunks and stems. Piling it against bark traps moisture and invites rot, which is the most common way a well-mulched bed kills the plant it was meant to protect.

Organic mulch breaks down. Expect to top up by an inch or so each year rather than starting from bare soil again.

Enter the bed dimensions and how deep you want the mulch, and it gives you cubic yards for bulk delivery and bag count for the garden centre. Depth is the input people get wrong — two to three inches suppresses weeds, and much deeper starts to work against the plants.

Why use this tool?

Depth that suits the bed

Two to three inches is the weed-suppressing range. The field goes deeper if you need it, but the guidance sits right next to it.

Bulk and bagged

Cubic yards for a delivered load, bags for a car boot. The comparison usually settles the question on the spot.

Any bag size

Two cubic feet is standard, but three cubic foot bags exist. Enter what your supplier sells.

Volume shown in both units

Cubic feet and cubic yards are both itemised, because suppliers quote in one or the other with no consistency.

How this mulch calculator works

Volume is the bed area multiplied by the depth in feet, so the inches you enter are divided by twelve first. The cubic feet figure is then divided by 27 for cubic yards, and by your bag size for a bag count.

There is no waste allowance here, and that is deliberate. Mulch is spread rather than cut, so nothing is lost to offcuts — the only overage is what settles slightly deeper in the low spots, which the rounding up to whole bags already covers.

The bulk crossover arrives around two cubic yards. That is roughly 27 two-cubic-foot bags, which is both a lot of plastic and a meaningful price difference; beyond it the saving on bulk grows steeply while the effort of spreading stays the same either way.

How to use it

  1. Step 1: Measure the bed

    Length and width. Curved and irregular beds are best approximated as the rectangle that would contain them, then trimmed slightly by eye.

  2. Step 2: Choose a depth

    Two inches for a bed you top up annually, three for a fresh application over bare soil or where weeds are a real problem.

  3. Step 3: Compare bulk against bags

    If the cubic yard figure is above about two, price a bulk delivery before buying bags.

  4. Step 4: Keep it off the stems

    When spreading, pull the mulch back from trunks and stems rather than piling it against them.

Example usage

A 20 by 8 foot border
160 square feet at 3 inches is 40 cubic feet, or 1.48 cubic yards — 20 two-cubic-foot bags. Right at the edge where bulk starts to make sense.
Refreshing an established bed
The same border at 1 inch to top up existing mulch is 13.3 cubic feet, or 7 bags. Annual top-ups are far cheaper than starting from bare soil each spring.
A large front garden
600 square feet at 3 inches is 150 cubic feet, or 5.6 cubic yards. That is 75 bags — the point at which bulk delivery is not really a choice.

Frequently asked questions

How deep should mulch be?

Two to three inches is the working range. That is enough to block light from weed seeds and slow moisture loss, without sealing the soil. Beyond about four inches you risk starving roots of air and keeping the surface permanently damp.

How many bags of mulch are in a cubic yard?

Thirteen and a half three-cubic-foot bags, or about 27 two-cubic-foot bags — the standard size in most garden centres.

When is bulk mulch worth it?

Around two cubic yards, or roughly 27 standard bags. Below that the delivery charge usually outweighs the saving; above it the gap widens quickly and you avoid disposing of a pile of plastic.

Why should mulch not touch tree trunks?

Piling it against bark holds moisture against tissue that needs to stay dry, which invites rot and pests and can girdle a young tree. Leave a few inches of clear ground around the base.

How often does mulch need replacing?

Organic mulches break down into the soil, which is part of the point. Expect to add an inch or so annually rather than stripping and replacing — that is both cheaper and better for the bed.

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