How much mulch do I need for my garden bed?

Multiply the bed area by the depth to get a volume. For a rectangular bed in metric that is length × width × (depth in mm ÷ 1000) cubic metres; in imperial it is length × width × (depth in inches ÷ 12) cubic feet, which you then divide by 27 to get cubic yards. This calculator does all of that across every bed at once and adds a waste allowance.

How deep should I lay mulch or topsoil?

Bark and wood mulch are usually laid 50–75 mm (2–3 in) deep to suppress weeds and hold moisture. New topsoil for lawns is typically 100–150 mm (4–6 in), and a thin compost top-dress is around 25 mm (1 in). Deeper layers smother roots, so match the depth to the job.

How many bags of mulch are in a cubic yard?

A cubic yard is about 765 litres or 27 cubic feet. A common 2 cubic foot bag means roughly 13.5 bags per cubic yard; a 60 litre bag means about 12.7 bags per cubic yard. The calculator divides your total volume by your chosen bag size and always rounds up to whole bags.

Is it cheaper to buy mulch in bags or in bulk?

Bulk loose delivery is almost always cheaper per cubic yard once you need more than roughly one cubic yard, because you avoid the packaging cost. Bags win for small jobs or when you cannot take a tipped delivery. Enter both prices and the tool tells you which is cheaper for your exact volume.

Why does the calculator add a waste percentage?

Loose material settles and compacts after spreading, beds are rarely perfectly level, and some is always lost in handling. A 5–10% allowance means you order enough in one go instead of running short. Set it to 0 if you want the exact geometric volume.

How much does a cubic yard of soil or mulch weigh?

It depends on the material and moisture. Bark mulch is light at roughly 270 kg per cubic yard, compost around 420 kg, while topsoil is much heavier at about 1,000 kg (one tonne) per cubic yard. The calculator estimates total weight from the material you pick so you can check your vehicle or barrow can handle the load.

Mulch & Soil Calculator

A combined mulch and soil calculator that turns one or more garden beds into the volume of material you actually need to buy — in cubic yards, cubic metres and litres — then tells you how many bags that is and what it will cost bagged versus bulk. It is built for anyone topping up borders, laying a new lawn, filling raised beds or mulching around trees, and it handles a whole garden of differently sized beds in a single pass.

How it works

Every bed is reduced to an area and then a volume. For a rectangular bed the area is length times width; for a circular bed it is pi times the radius squared, where the radius is half the diameter you enter. The chosen depth is converted into the same length unit as the surface — millimetres become metres, inches become feet — and multiplied by the area to give a raw volume per bed.

The raw volumes from all of your beds are added together, then a waste and settlement allowance (5% by default) is applied so you order enough to cover compaction and uneven ground. That single total is expressed every way a supplier might quote it: cubic metres, cubic yards, litres and a rounded-up bag count based on the bag size you enter. A material density is used to estimate the total weight, which matters when you are checking whether a load fits in a car boot, a trailer or a wheelbarrow run.

Finally the calculator runs a quick cost comparison. It multiplies the bag count by your price per bag, multiplies your bulk rate by the volume, and highlights the cheaper route. Bulk loose delivery usually wins above roughly a cubic yard because you stop paying for plastic and packaging; bags win for small top-ups. Because the maths is all geometry and arithmetic, every figure recalculates instantly as you type, and nothing ever leaves your browser — your bed sizes and prices are saved only on your own device.

Worked example

Say you have two rectangular borders, each 4 m by 1.5 m, plus a circular bed 2 m across, all to be mulched 75 mm deep.

Border area: 4 × 1.5 = 6 m² each, so 12 m² for the pair.
Circle area: pi × 1² = 3.14 m².
Total area: about 15.14 m².
Volume at 0.075 m deep: 15.14 × 0.075 = 1.14 m³ before waste.
Add a 5% allowance: about 1.19 m³, which is roughly 1.56 cubic yards or 1,190 litres.
In 60 litre bags that is ceil(1190 / 60) = 20 bags.

At £5.99 a bag that is about £120, while bulk at £45 per cubic metre is about £54 — so a bulk delivery saves around £66 here.

Reference: formula and densities

Volume (m³) = area (m²) × depth (m), with depth (mm) ÷ 1000 for metric or depth (in) ÷ 12 then ÷ 27 for imperial cubic yards.

Conversions used: 1 cubic yard = 27 cubic feet = 0.7646 cubic metres = 764.6 litres. Typical loose densities applied for the weight estimate are bark mulch 350, compost 550, garden soil 800, topsoil 1300, gravel 1600 and rubber mulch 480 kilograms per cubic metre. These are averages; wet material weighs more, and graded stone varies, so treat the weight as a planning guide rather than an exact figure.