Mulch calculator

How much mulch do I need for a 10 × 10 ft bed?

About one cubic yard. A 10 ft by 10 ft bed at 3 in holds 25 cu ft of mulch, and with 10% added for settling the calculator shows 27.5 cu ft, or 1.02 cu yd. In bags, that is 19 of the 1.5 cu ft size, 14 of 2 cu ft or 10 of 3 cu ft.

Metric mode opens on a 3 m by 3 m bed at the RHS ideal of 7.5 cm. That is 0.675 m³ before settling and 0.74 m³ after, which is 13 bags of 60 L or 2 of the 0.6 m3 bulk bags.

Measure the planted area you will actually cover. For a border, the length along the front and the average depth back to the fence or wall is usually close enough. For a ring around a tree, use the circle shape and enter the full width of the ring, not the radius. If you already know the area from a plan or another calculator, the I know the area option skips the measuring step.

How does the calculator work out mulch volume and bags?

Volume is area times depth, with the depth turned into the same unit as the area. In US mode: length (ft) × width (ft) × depth (in) ÷ 12 = cubic feet, and cubic feet ÷ 27 = cubic yards. For a circle the area is π × (diameter ÷ 2)². The settling allowance multiplies the volume, and each bag count is the volume with settling divided by the bag size, rounded up.

Metric mode has a neat shortcut, because one square metre covered one millimetre deep is exactly one litre. So 10 m² at 75 mm is 750 litres before settling, and the bag count is litres ÷ bag litres. That makes UK bag labels, which are in litres, easy to check by hand.

Worked example: a long border at the upper depth

A 200 sq ft border at 4 in, with 5% for settling. 200 × 4 ÷ 12 = 66.67 cu ft; × 1.05 = 70 cu ft; ÷ 27 = 2.59 cu yd. Bags: 70 ÷ 1.5 = 46.7, so 47; 70 ÷ 2 = 35; 70 ÷ 3 = 23.3, so 24.

If your bags are a size the calculator does not list, type it in the Your bag size box. A 3 in bed of 100 sq ft with 10% settling takes 11 bags of 2.5 cu ft.

Which mulch depth should I choose?

For trees and shrubs on well-drained soil, 3 in, which is the calculator's US default. Around trees and shrubs on well-drained soil, 3 in (75 mm) is the low end of the 3-4 in layer Iowa State and Mississippi State recommend. On heavy clay or soggy ground, go thinner. On heavy clay or poorly drained soils keep mulch to about 2 in (50 mm): Rutgers caps it at 2 in and Iowa State advises 2-3 in. The upper preset is a ceiling, not a target: Penn State says mulch should be no thicker than 3-4 in; Rutgers says total depth, including old mulch, should not exceed 3 in.

The sources do not agree exactly, so the calculator offers each figure with its source rather than averaging them. In the UK, the RHS works in centimetres. The RHS says organic mulches should be at least 5 cm (2 in) thick. The RHS says organic mulches are ideally 7.5 cm (3 in) thick. Fine-textured materials such as shredded leaves or compost go on thinner still. Rutgers advises fine-textured mulches be applied in 1-2 in layers.

A common belief is that more mulch protects plants better. Extension services say the opposite: deep layers and mulch piled against trunks keep air and water from roots and invite rot. Keep mulch off trunks and stems: Iowa State says at least 6 in from tree trunks; Rutgers says 3-5 in from young stems and 8-12 in from mature trunks. If you choose a custom depth beyond 4 in, the result carries a warning.

The research on depth is thinner than the advice suggests. A 2026 systematic review screened 1,200 papers and found only 11 peer-reviewed studies that tested mulch depth on trees; all but two tested depths above the usual 5–10 cm (2–4 in), and harms were reported mostly above 10 cm (Martin et al., Arboriculture & Urban Forestry). On weeds, one greenhouse trial is often quoted: In a University of Florida greenhouse trial, 2 inches of hardwood chip mulch alone cut garden spurge growth by 87% and eclipta by 83%, against 51% and 45% for 1 inch, per Saha et al., HortTechnology (2019). That is one trial with potted weeds, not a field rate, but it supports staying at the depths above rather than going thinner to save money. The mulch depth and coverage guide goes through depth plant by plant.

Why does the calculator add 10% for settling?

Because fresh bark settles once it is spread and watered, and the only figure we found for how much comes from a UK mulch producer. Melcourt recommends allowing 5-10% extra bark mulch for natural settlement. The calculator starts at the top of Melcourt's range. No extension service we checked gives a settling percentage, so treat this as one producer's advice and lower it for fine, already-composted material.

Topping up an old bed is different. Rutgers says the depth limit includes the mulch already there, so measure what is left and enter only the difference as the depth. Ordering a full new layer on top of last year's is how beds end up too deep.

Illustration sources

• Melcourt Industries Ltd (UK) — Ornamental Bark Mulch product page (specification and how to use)

How many bags of mulch fit in a cubic yard?

It depends on the bag, and US bags come in several sizes. The calculator lists three. Scotts Nature Scapes mulch is sold in 1.5 cu ft bags (42.5 L); one covers 6 sq ft 3 in deep. A common US mulch bag holds 2 cu ft (56.6 L); Scotts' label says it covers 8 sq ft 3 in deep. Some US bark mulch is sold in 3 cu ft (85 L) bags, which cover 12 sq ft 3 in deep. The 3 cu ft size is a single-source value: the only listing we found was a retailer's, with no maker's data sheet behind it, so check the bag before you rely on that count.

The 2 cu ft label is a useful check on the arithmetic. A 2 cu ft bag spread 3 in deep covers 8 sq ft, as printed on Scotts Nature Scapes mulch bags. The calculator's formula gives the same answer, which is a quick way to confirm you have entered the depth in inches.

Bags or bulk mulch: what changes in the UK?

In the US, bulk mulch is sold by the cubic yard and bags by the cubic foot, so the calculator shows both. Above a cubic yard or so, the bag count gets long: the 200 sq ft border above needs 35 bags of the common size. We hold no price data, so the calculator cannot say where bulk becomes cheaper; that depends on your supplier's yard price and delivery charge. Price the cubic-yard figure against the bag count from the same result.

UK results switch to litres and bulk bags, using Melcourt's sizes. Melcourt bark mulches are sold in 60 litre (2.1 cu ft) bags. Melcourt's bulk bags hold 0.6 m3 (21 cu ft, 0.78 cu yd) of mulch. Other UK bark bags come in other sizes, but we found no maker's page listing them, so enter yours in the bag-size box in litres. Depth is in millimetres, and the presets follow the RHS.

Bark is now a large part of UK garden products, not just mulch. Wood fibre (1,055,510 m³) and bark (365,792 m³) together made up 45.1% of UK growing media volume in 2023, more than peat, per Defra's growing media datasheets.

When is the mulch result wrong?

• Old mulch still in the bed. The calculator assumes bare soil. Subtract what is there from the depth you enter.
• Stone or rubber mulch. These do not settle like bark and are bought by weight; for stone, use the tons of gravel for your area calculator instead.
• Steep banks. Mulch washes down slopes, so the top of the bank thins and the bottom thickens. Expect to top up.
• Weight for a trailer. The calculator gives volume only. We have no sourced weight for mulch, as the material weight and density table notes, and wet bark is far heavier than dry.
• New beds needing soil first. If the bed needs soil before mulch, size that layer with the cubic yards of soil or dirt calculator.

How much yard waste becomes mulch?

A lot of it starts as garden waste. Americans generated 35.4 million tons of yard trimmings in 2018 (12.1% of municipal solid waste), of which 22.3 million tons (63%) were composted, per EPA's Facts and Figures; 2018 is still EPA's latest national year and mulch spread directly on land is not counted. The rest goes elsewhere: 10.5 million tons of US yard trimmings were still landfilled in 2018, per EPA's Facts and Figures (the latest national year). Chipping your own prunings into the beds keeps them out of both figures, and the volume formula works the same for homemade chips as for bagged bark.

Which calculator or guide do I need next?

Before mulching a new bed, check the soil beneath. The guide to topsoil depth for lawns and beds sets out how deep the growing layer should be, and the topsoil calculator turns that into cubic yards or bulk bags. For gravel paths between beds, use the gravel calculator, which works by weight. The landscaping calculators page lists the rest, including paving and fencing.

Mulch calculator questions

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