Volume first, then bags
Mulch, gravel, soil and concrete are all sold by the cubic yard, but the space you need to fill is measured in feet and inches. This calculator does the one conversion that matters — length × width × depth into cubic yards (divide cubic feet by 27) — then adds your waste allowance and, for concrete work, translates the result into pre-mix bags: an 80 lb bag yields about 0.6 cubic feet, a 60 lb bag about 0.45, and a 40 lb bag about 0.3.
Depth is where mistakes happen: 4 inches is 0.333 feet, not 0.4. This page takes depth in inches (or cm) precisely so you never have to make that conversion yourself.
Why the waste allowance?
No excavation is exact: the ground undulates, forms bow out, soil compacts, and some material always spills or stays in the wheelbarrow. Ordering exactly the geometric volume guarantees coming up short mid-job. Ten percent extra is the standard planning allowance for flat, well-defined areas; bump it to 15% for rough ground or irregular shapes. The headline figure includes the waste allowance; the exact geometric volume is shown alongside it.
Worked example
A pad 10 ft × 10 ft at 4 inches deep: 10 × 10 × 0.333 = 33.33 cubic feet = 1.23 cubic yards. With 10% waste, order 1.36 cubic yards — or, in bags, 62 × 80 lb bags, which is exactly the point at which most people switch to a ready-mix delivery.
How to use this calculator
- Choose imperial or metric units.
- Measure the length and width of the area, and the depth you need to fill.
- Set the waste allowance — 10% is a sensible default.
- Read the cubic yards to order, and the bag counts if you are mixing it yourself.
- For material-specific estimates, follow up with the Concrete, Gravel, Sand or Mulch calculators.
Bags vs ready-mix: the crossover
Bags win on small jobs — a few post holes, a single step, patch repairs — because there is no delivery fee and no clock ticking on a drum. Past roughly one cubic yard (about 45–60 bags depending on size), the maths usually flips: your time mixing, the per-bag price premium and the risk of cold joints between batches start to outweigh a short-load delivery. The bag counts here are shown all three ways so you can price the job both ways before committing.