Mulch Calculator

How to use this calculator

1. Measure each bed; for curvy beds, estimate an average width or use the area option.
2. Choose a depth: 2–3 in (5–7.5 cm) is typical; don't pile mulch against stems and trunks.
3. Pick the bag size sold near you, or use the cubic yards/m³ figure for bulk delivery.
4. Add 5–10% under Advanced if your mulch is fresh and will settle.

Method & assumptions

Volume (cu ft) = Area (sq ft) × Depth (in) ÷ 12
Cubic yards = cu ft ÷ 27
Bags = Volume ÷ bag size, rounded up

Depth

finished mulch depth

Bag size

2 or 3 cu ft (US), 50/70 L (UK/AU)

Assumptions & limits

• Existing old mulch is not counted; measure only the new depth.
• Bulk mulch is sold by loose volume.

Rounding: purchase quantities are always rounded up to whole bags, boxes, sheets or bundles. See our methodology.

Worked examples

In depth: mulch planning notes

Choosing a depth

Most garden beds do well with 2–3 in (5–7.5 cm) of mulch. Less than 2 in lets weeds through; more than 4 in can keep soil too wet, starve roots of air and encourage rot where mulch touches stems. Around trees, keep mulch a few inches away from the trunk — the "mulch volcano" piled against bark is a common cause of damage. Paths and play areas use deeper layers: wood chips under swings are often laid 9–12 in deep for impact attenuation, following playground safety guidance.

If you are topping up existing mulch, measure the depth that is already there and only add the difference. Fine mulches break down faster and need topping up each year; coarse bark nuggets last longer.

Bags or bulk?

Bagged mulch is sold by volume — usually 2 cu ft or 3 cu ft bags in the US and 50–80 L bags in the UK and Australia. Bulk mulch is sold by the cubic yard or cubic meter, often with delivery. As a rule of thumb, once you need more than about 2 cubic yards (40 or so bags), bulk is cheaper and quicker, but you need somewhere to tip it and a wheelbarrow to move it.

Loose mulch settles after spreading and rain, so the calculator adds a modest allowance. Bark that has been sitting in a wet pile is heavier than dry mulch; volume is what matters for coverage, not weight. If you are mulching over landscape fabric or cardboard sheet-mulching, the depth can be a little thinner because the barrier does some of the weed suppression.

Dyed mulches, rubber mulch and stone all have different properties. Stone is estimated by weight, so use the gravel calculator for decorative rock.

When to mulch

Late spring, once the soil has warmed, is a good time to mulch most beds; mulching cold soil keeps it cold for longer. A second top-up in autumn insulates roots over winter. Water the bed before spreading mulch so it locks in moisture, and pull weeds first — mulch suppresses new weeds but does not kill established ones.

Tips & common mistakes

• Too much mulch can suffocate roots — more is not better beyond about 3 in.
• Bulk is usually cheaper per yard above 2–3 cu yd, but check delivery fees.
• Lay mulch after weeding and watering, not before.

Sources

1. Penn State Extension – mulching landscape plants — checked 2026-10; verify before launch
2. University of Minnesota Extension – mulch for the garden — checked 2026-10; verify before launch
3. RHS (UK) – mulches and mulching — checked 2026-10; verify before launch

Default values (bag yields, coverage rates, densities) are typical figures from manufacturer literature. Always check the label on the product you buy.

Cite or embed this calculator

DIYCalcLab. “Mulch Calculator.” Oct 18, 2026. https://diycalclab.com/landscaping/mulch-calculator/

An embeddable version for blogs and contractor sites is planned.