How we calculate
Every estimate on Bulk Material Calculator is the same three steps, done in a fixed order so the arithmetic is auditable. This page sets out the formulas, the density figures we use, why the results are estimates rather than guarantees, and the standards and manufacturer data the numbers come from.
Step 1 — area
The area of the surface you are covering, in square feet, with every dimension converted to feet first:
- Rectangle or square: length × width
- Circle: π × (diameter ÷ 2)²
- Triangle: ½ × base × height
- Ring or border: π × (outer radius² − inner radius²)
If you set the number of identical areas, the area is multiplied by that count before anything else.
Step 2 — volume
Volume in cubic feet is area × depth, with the depth converted to feet (so 3 inches becomes 0.25). Cubic feet ÷ 27 gives cubic yards; cubic feet × 0.0283 gives cubic metres. The cubic-yard figure is the one most suppliers quote.
Step 3 — weight, bags and cost
Weight in tons is cubic yards × the material's density in tons per cubic yard. Bag counts are volume in cubic feet ÷ the yield of one bag, rounded up. Cost is the quantity in your chosen unit (cubic yards, tons or bags) × the price you enter. Each of these is also shown with the waste allowance added.
The density figures
These are typical delivered, settled densities for each material in its normal sold state, dry unless noted. Real deliveries vary ±10–15% with moisture and compaction — the single biggest reason the results are estimates.
| Material | lb / ft³ | tons / yd³ | Sold by | Typical use |
|---|---|---|---|---|
| Pea gravel (3/8″, rounded) | 100–105 | 1.35 | ton or yd³ | Paths, patios, dog runs, drainage |
| #57 crushed stone (3/4″, washed) | 100–105 | 1.35 | ton | Drainage, slab sub-base, French drains |
| 3/4″ minus / dense-grade | 105–115 | 1.45 | ton | Driveway base, paver base, road pack |
| Crushed concrete (RCA) | 100–110 | 1.35 | ton | Driveway base, structural fill (cheaper) |
| River rock (1–3″) | 95–105 | 1.40 | ton or yd³ | Dry creek beds, borders, xeriscape |
| Decomposed granite | 110–120 | 1.50 | ton | Paths, patios, natural-look driveways |
| Road base / Class 5 | 110–120 | 1.50 | ton | Compacted base under pavers, slabs, drives |
| Material | lb / ft³ | tons / yd³ | Sold by | Typical use |
|---|---|---|---|---|
| Screened topsoil (dry) | 75–85 | 1.10 | yd³ (some ton) | New lawns, bed top-up, levelling |
| Topsoil (moist) | 95–110 | 1.40 | yd³ | As delivered after rain — weighs more |
| Fill dirt / structural fill | 90–100 | 1.25 | ton or yd³ | Raising grade, backfill, berms |
| Compost | 40–50 | 0.55 | yd³ or bag | Bed amendment, lawn top-dressing |
| Garden / raised-bed mix | 65–80 | 1.00 | yd³ or bag | Filling raised beds (soil + compost blend) |
| Material | lb / ft³ | tons / yd³ | Sold by | Coverage per yd³ |
|---|---|---|---|---|
| Shredded hardwood / bark | 18–22 | 0.45 | yd³ or 2 ft³ bag | ~160 ft² at 2″, ~108 ft² at 3″ |
| Wood chips (arborist) | 15–20 | 0.40 | yd³ | ~160 ft² at 2″ |
| Rubber mulch (playground) | 35–50 | 0.63 | bag or pallet | ~2 ft² per ft³ at 6″ |
| Pine straw | n/a | n/a | bale | ~40–50 ft² per bale |
| Compost mulch | 40–50 | 0.55 | yd³ | ~160 ft² at 2″ |
| Product | Yield | Per cubic yard | Best for | Notes |
|---|---|---|---|---|
| Ready-mix (delivered) | 1 yd³ per yd³ | — | Slabs, driveways, footings > ½ yd³ | Short-load fee under ~1 yd³ |
| 80 lb bag | ~0.60 ft³ | 45 bags | Small pads, posts, repairs | ~4,000 psi mixed |
| 60 lb bag | ~0.45 ft³ | 60 bags | Post setting, small footings | Common fence-post size |
| 50 lb bag | ~0.375 ft³ | 72 bags | Small repairs | |
| 40 lb bag | ~0.30 ft³ | 90 bags | Patching, setting small posts | |
| Cured concrete weight | — | ~4,000 lb (2 tons) | — | 145–150 lb/ft³ |
Common quantities at a glance
| Quantity | Works out to |
|---|---|
| 1 cubic yard | 27 cubic feet · 0.765 cubic metres · 202 US gallons |
| 1 cubic yard covers | 324 ft² at 1″ · 162 ft² at 2″ · 108 ft² at 3″ · 81 ft² at 4″ |
| 1 ton of gravel covers | ~100 ft² at 2″ · ~50 ft² at 4″ (≈1.4 tons per yd³) |
| 1 cubic yard of mulch | 13.5 bags of 2 ft³ · covers ~160 ft² at 2″ |
| Concrete for a 10×10 slab | 4″ ≈ 1.23 yd³ · 6″ ≈ 1.85 yd³ |
| 80 lb concrete bags per yard | 45 · (60 lb = 60 bags · 40 lb = 90 bags) |
| Cubic feet → cubic yards | divide by 27 |
| Cubic yards → tons | multiply by density (gravel 1.4 · sand 1.35 · topsoil 1.1 · concrete 2.0 · mulch 0.5) |
| Standard tandem dump truck | 10–14 cubic yards (≈15–20 tons) |
| Recommended over-order | 10% for settling, compaction and spillage (15% for driveways) |
Why the results are estimates
Bulk material is not a manufactured product with a spec sheet. The same gravel pit sells stone that weighs differently in July and in November. Mulch settles by a fifth in its first season. Topsoil delivered the morning after rain can weigh a third more than the same soil in a dry week. We publish mid-range figures, show the density each result used, and default to ordering 10% extra so a normal variation does not stop your job.
Sources
| Source | What it informs |
|---|---|
| ASTM C29 / C29M | Standard test method for bulk density (unit weight) of aggregate — the basis for the lb/ft³ figures. |
| ASTM D448 / #57, #8 stone gradations | Standard sizes of coarse aggregate, used for the stone descriptions. |
| ASTM C33 | Concrete aggregate spec — defines the coarse "concrete sand" specified for paver bedding. |
| Manufacturer bag data (Quikrete, Sakrete) | Published yields for 40 / 50 / 60 / 80 lb pre-mix bags (0.30–0.60 ft³). |
| NRMCA / ready-mix industry figures | Fresh and cured concrete unit weight (~145–150 lb/ft³, ~4,000 lb per yd³). |
| USDA & extension-service guidance | Mulch and topsoil depths for lawns, beds and trees. |
| Landscape-supply density tables | Cross-checked delivered densities for mulch, soil, river rock and decomposed granite. |
Figures are reviewed against these sources on publication and rechecked when a user reports a discrepancy. Last reviewed 2026-09-07. Spot an error? Email hello@bulkmaterialcalculator.com with the inputs you used and the number you expected.