How we calculate
Every figure this site uses, in one place — so you can check any result against your own supplier's numbers.
Last updated
The basic method
Loose material is volume: area multiplied by depth. Everything else is unit conversion. A 20 by 10 foot bed at 3 inches deep is 200 × 0.25 = 50 cubic feet, and since a cubic yard is 27 cubic feet, that is 1.85 cubic yards.
Products sold by coverage — flooring, sod, paint, drywall — work the other way: total area divided by the area one unit covers, then rounded up. Products applied at a rate, like seed and fertiliser, multiply area by pounds per 1,000 square feet.
Units and conversions
All arithmetic happens internally in metric base units — metres, square metres, cubic metres and kilograms — and is converted for display. That means switching between imperial and metric never introduces a rounding drift, and the same formula serves both.
Conversions use the exact international definitions: 1 inch = 25.4 mm, 1 pound = 0.45359237 kg. A US short ton is 2,000 pounds; a metric tonne is 1,000 kg. Gallons are US liquid gallons.
Material densities
Bulk densities are loose, as-delivered, mid-range values. Real material varies with moisture content and grind — wet mulch can weigh half again what dry mulch does — so treat weights as estimates for checking vehicle limits, not as billing figures.
| Material | Assumed density |
|---|---|
| Mulch (shredded bark) | 800 lb/yd³ |
| Bark nuggets | 700 lb/yd³ |
| Wood chips | 600 lb/yd³ |
| Compost | 1,000 lb/yd³ |
| Topsoil (screened) | 2,200 lb/yd³ |
| Sand (dry) | 2,700 lb/yd³ |
| Decorative / river rock | 2,700 lb/yd³ |
| Gravel and pea gravel | 2,800 lb/yd³ |
| Crushed rock | 2,900 lb/yd³ |
| Crushed base / crusher run | 3,000 lb/yd³ |
| Concrete (cured) | 4,050 lb/yd³ |
Rounding
Anything you buy in whole units — bags, pavers, sheets, boards, posts — is always rounded up. Rounding a bag count down would be actively harmful advice. Volumes, areas and weights are shown to two decimal places without rounding up, because suppliers sell partial yards.
Bag counts are guarded against floating-point error, so a job needing exactly 40 bags reports 40 rather than 41.
Waste allowances
Each calculator defaults to the allowance conventional for that trade: around 5% for bulk landscape material you can top up later, 10% for concrete and pavers, 10 to 15% for tile and flooring where cuts waste whole pieces, and 20% for compacted base material, which loses 15 to 20% of its loose volume when tamped. Every allowance is editable, and the figure used is stated on the page.
What these calculators are not
They are estimating tools for planning and shopping. They are not structural design, and nothing here substitutes for local building code, a permit, or an engineer where one is required — footing depth, beam sizing, joist spans and load calculations all depend on factors this site cannot see.
Confirm quantities with your supplier before ordering. If you find an error, tell us — corrections are the fastest way to make Project Calculator better.