Methodology and Sources
Methodology and Sources for BuildCalc.
This page sets out where the numbers on BuildCalc come from, so you can check them rather than take them on trust. If a figure on a calculator page cannot be traced back to something on this page, that is a bug — tell me.
The core formula
Every volume calculator on this site uses the same arithmetic, with no hidden correction factors:
volume (ft³) = length (ft) × width (ft) × depth (in) ÷ 12
volume (yd³) = volume (ft³) ÷ 27
weight (lb) = volume (ft³) × bulk density (lb/ft³)
ordered = volume × (1 + waste %)
There are 27 cubic feet in a cubic yard (3 × 3 × 3). Cubic metres are converted at 1 ft³ = 0.0283168 m³.
The only judgement calls in the whole calculation are the three material-specific inputs: bulk density, waste allowance and default application depth. Those are listed in the table below and are stated on every result.
Material coefficients used
| Material | Bulk density (lb/ft³) | Default waste | Source basis |
|---|---|---|---|
| Concrete (normal weight) | 150 | 5% | Standard normal-weight concrete, 4,050 lb per cubic yard |
| Crushed stone / gravel | 105 | 10% | Crushed aggregate, 2,835 lb per cubic yard |
| Mulch (bark, loose) | 25 | 5% | Loose bark mulch as delivered |
| Topsoil (screened, loose) | 90 | 10% | Loose screened loam, varies with moisture |
| Sand (masonry / concrete) | 100 | 10% | Dry sand; damp sand runs 10–15% heavier |
| Paver base (¾ in minus) | 105 | 10% | Crushed base with fines |
| River rock | 90 | 10% | Rounded decorative stone, 1–3 in grade |
| Fill dirt (unscreened) | 95 | 10% | Subsoil, minimal organic content |
| Sod | sold by area | 5% | Sold by the square foot or pallet |
Bag yields: an 80 lb bag of concrete mix yields approximately 0.6 ft³, and a 60 lb bag approximately 0.45 ft³. These are manufacturer-published yields for standard mixes; high-strength and fast-setting mixes differ.
Where the densities come from
Bulk density ranges are published by aggregate suppliers, state transportation departments in their material specifications, and standard civil engineering references. For any given material the real figure varies by source, gradation and moisture — often by 10% or more. The values above are mid-range figures for the material as typically delivered, which is the right choice for an order estimate but not for a load calculation.
If your supplier quotes a specific density, use it. The waste field is the easiest place to absorb the difference.
Waste and compaction allowances
- 5% — flat work on well-compacted, formwork-controlled ground. Concrete slabs, screeded sand.
- 10% — footings, driveways, anything with an irregular edge, and any loose material that will compact. Crushed stone compacts up to 20% under traffic; the default allowance covers the difference between the loose volume you order and the depth you want after compaction.
- Settling — topsoil and fill dirt settle 15–25% in their first season as they compact and rain moves through them. Both calculators note this on the result, and fill dirt guidance recommends placing in compacted lifts rather than one deep dump.
Depth guidance
Application depths come from common construction practice for residential work — the values listed on each material page. The two that matter most:
- Concrete slab thickness changes with load, not with area. 4 inches for patios, walkways and shed slabs; 5–6 inches reinforced for a car driveway; 6–8 inches for anything heavier.
- Paver base depth changes the same way: 4 inches compacted for foot traffic, 6 inches for cars, 8 inches for heavier vehicles.
None of this is a substitute for local code. Frost depth in particular is set locally and can be well over 12 inches in northern states.
Prices
Default prices are US national averages for material only, and they are labelled as such everywhere they appear. They exclude delivery, short-load and minimum-order fees, pump trucks, equipment rental, labour and sales tax.
Regional variation is large — the same cubic yard of ready-mix concrete can be $130 in one market and $210 in another. Type your own price into the calculator. That field exists precisely because the default is not a quote.
Corrections
Material data varies by region and by supplier, and I would rather fix a number than defend it. Send corrections, with a source if you have one, to hello@wang11.xyz or through the contact page. Corrections are applied to the underlying data file and the site is rebuilt, so the change applies everywhere that number is used.
Data last reviewed: 2026-10-01.