Every default value in our calculators was chosen based on industry guidelines and common practice. You can adjust all of these on the calculator pages. Here's what each default is and why we chose it.
Rounding rules
We always round up to the nearest whole bag, box, pallet, or sheet. You cannot buy fractions of a unit, and running short mid-project forces an extra trip to the store. The waste factor already accounts for over-ordering; the rounding-up is an additional safety margin of at most one unit.
Default depths
| Material | Default depth | Why |
|---|
| Mulch | 3 inches | University extension service recommends 2–3" for established beds; 3" is sufficient for weed suppression without smothering roots |
| Gravel (decorative) | 2 inches | Minimum depth for stable decorative coverage; most landscape paths use 2–3" |
| Topsoil | 4 inches | Standard for new garden beds; enough to support annual plant growth |
| Sand (paver base) | 1 inch | Industry standard bedding layer for paver installation (ICPI guidelines) |
| Concrete slab | 4 inches | IRC minimum for residential slabs (driveways, patios, walkways) |
Default waste factors
| Material / pattern | Default waste | Why |
|---|
| Mulch (straight beds) | 5% | Minimal waste for regular shapes; accounts for slight unevenness |
| Gravel, sand | 10% | Accounts for compaction, spillage, and irregular edges |
| Concrete | 10% | Accounts for spillage, pump waste, and uneven subgrade |
| Flooring (straight) | 10% | NWFA guideline for straight-layout hardwood and laminate |
| Flooring (diagonal) | 15% | NWFA guideline; more cuts at room edges increase waste |
| Tile (straight) | 10% | TCNA Handbook recommendation for straight-grid tile |
| Tile (diagonal) | 15% | TCNA Handbook; more corner cuts needed |
| Drywall | 12% | Accounts for outlet/switch cutouts, door/window trimming, and breakage |
| Paint | 10% | Accounts for roller/brush waste and touch-ups |
Door and window deductions (paint & drywall)
| Opening | Deduction | Why |
|---|
| Standard door (3 × 7 ft) | 21 sq ft | Exact: 3 × 7 = 21 |
| Standard window (3 × 5 ft) | 15 sq ft | Exact: 3 × 5 = 15 |
Important caveats
- All calculations are estimates. Material densities vary with moisture content and compaction.
- Coverage rates for paint depend on surface texture, porosity, and application method.
- For large orders, always confirm quantities with your local supplier before buying.
- Regional product variations (bag sizes, pallet standards) may differ from our defaults.