Depth is the variable that decides the order
Every bulk garden material is area × depth, and the depth is a horticultural decision, not a rounding. Mulch needs 5–8 cm (2–3 in) to suppress weeds and hold moisture; thinner and the weeds come through, thicker and you starve the roots of air — and mulch piled against a trunk will rot it. Topsoil for a new lawn wants 10–15 cm, and a raised bed wants filling to within a few centimetres of the rim. One cubic yard covers about 100 ft² at 3 in deep, or 300 ft² at 1 in. In metric, one cubic metre covers 10 m² at 100 mm. Those two conversions answer most bulk-material questions on their own.
Bags or bulk, and where the crossover sits
Bagged material is convenient and expensive; bulk is cheap and arrives in a heap on your driveway. A standard 2 ft³ bag of mulch means 13.5 bags to the cubic yard — so beyond roughly three cubic yards, bulk delivery almost always wins even after the delivery fee, and it wins on your back long before it wins on price. Weight matters when you are hauling: mulch runs 400–800 lb per cubic yard, dry topsoil about 2,000 lb, and wet topsoil considerably more. A half-tonne pickup cannot legally or safely carry a cubic yard of wet soil, whatever the load bed suggests.
Raised beds and soil mixes
A raised bed is a volume, not an area: length × width × fill depth, and fill depth is the inside height minus the 3–5 cm of freeboard you leave so watering does not wash the mix over the edge. Do not fill it with topsoil alone — it compacts, drains badly and sets like a brick. The classic blend is roughly one third compost, one third coarse sand or vermiculite and one third topsoil or peat-free equivalent; Mel's Mix is one third each of compost, vermiculite and peat. Expect the mix to settle 10–20% in the first season, so either overfill slightly or plan to top up in the spring. Curved and oval beds are easier to size by treating them as an ellipse: π × a × b × depth.
Lawns: seed by the rate, sod by the pallet
Grass seed is sown at a rate, and the rate depends on what you are doing and what you are sowing: a new lawn wants roughly double the overseeding rate, and a fine fescue goes down heavier than a ryegrass. Typical new-lawn rates run 25–50 g/m² (roughly 5–10 lb per 1,000 ft²), with overseeding at about half. Sod is the impatient alternative: it is sold by the pallet, typically covering 400–500 ft² and weighing 1,500–3,000 lb depending on how wet it is, which is a real constraint on delivery and on how fast you must lay it. Add 5–10% to any sod order for the cuts around curves and beds, and lay it the day it arrives — a pallet of turf left standing in the sun for two days is compost.
