Methodology: how the calculators work
How the numbers on this site are calculated, and where the figures come from. Last reviewed October 2026.
The basic method
Every calculator turns your measurements into an area or volume, converts that into the unit suppliers sell by (cubic yards, tons, bags, boards or pallets), adds an optional allowance for waste, and rounds up anything sold whole. Nothing you type leaves your browser.
- Rectangle area = length × width. Circle area = π × (diameter ÷ 2)². Triangle area = ½ × base × height.
- Volume = area × depth, with all lengths in the same unit.
- Weight = volume × density.
- Bags = volume × (1 + waste) ÷ volume per bag, rounded up.
Unit conversions
| Conversion | Factor |
|---|---|
| 1 inch | 2.54 cm (exact) |
| 1 foot | 0.3048 m (exact) |
| 1 sq ft | 0.09290304 m² |
| 1 cubic yard | 27 cubic feet = 0.764555 m³ |
| 1 US ton | 2,000 lb = 907.185 kg |
| 1 pound | 0.45359237 kg (exact) |
Material densities
These are typical figures for planning. Density changes with moisture, gradation and quarry, so use your supplier's number when you have it (most calculators have a custom option).
| Material | Tons per cubic yard | Approx. lb per cubic foot |
|---|---|---|
| Crushed stone / road base | 1.4 | 104 |
| Pea gravel | 1.4 | 104 |
| #57 stone | 1.3 | 96 |
| Crushed limestone | 1.4 | 104 |
| River rock | 1.4 | 104 |
| Topsoil | 1.1 | 81 |
| Fill dirt | 1.3 | 96 |
| Compost | 0.5 | 37 |
| Mulch (wood, shredded) | 0.3 | 22 |
| Concrete (cured) | 2 | 148 |
| Dry sand (play, masonry, paver base) | 1.3 | 96 |
| Damp sand | 1.4 | 104 |
| Wet sand | 1.5 | 111 |
| Lava rock | 0.7 | 52 |
| Decomposed granite | 1.4 | 104 |
| White marble chips | 1.5 | 111 |
Concrete bag yields
| Bag size | Yield (cubic feet) |
|---|---|
| 40 lb | 0.3 |
| 50 lb | 0.375 |
| 60 lb | 0.45 |
| 80 lb | 0.6 |
Waste and extra
Defaults are 5% for mulch and sod, and 10% for most other materials. Typical ranges are 5–15%, higher for diagonal layouts, tight cuts, soft ground or compaction. You can change the allowance on every calculator.
Sources and limits
Conversion factors are the exact definitions published by NIST. Densities, bag sizes and pallet sizes are typical supplier and manufacturer figures; they vary by product and region and are not guarantees. Where a result matters, such as a structural pour, confirm quantities with your supplier and follow local code.
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