Methodology
Every number on this site traces to a published source or a stated model. The fastest way to distrust a calculator is to catch it hiding an assumption, and this page is the ledger.
Quantity Formulas & Waste Factors
Geometry is geometry; the expertise is in the allowances. Concrete ordering ranges follow NRMCA CIP 8 (Discrepancies in Yield): 4-10% over plan volume, because form deflection, subgrade irregularity, and spillage mean placed ≠ plan. Bag yields are manufacturer TDS values (e.g., QUIKRETE 60 lb ≈ 0.45 ft³). Waste factors that are industry convention rather than published guidance are labeled as such on the page that uses them: we do not launder folklore into fact. Rounding is always: net quantity → allowance → round up to the purchase unit.
Labor Cost Model (Modeled, Not Quotes)
Labor context is modeled, not observed pricing. The chain: BLS-published median wages (May 2024 OEWS medians via BLS OOH, read 2026-08-15) × a burden-and-markup band of 1.5-2.5×. The band decomposes as employer payroll taxes (FICA 7.65% + FUTA/SUTA), workers’ comp (trade class × experience modifier, since roofing runs far higher than finish work), benefits (BLS ECEC ≈ 30% of compensation), and contractor overhead & profit (NAHB-surveyed gross margins of roughly 21-30%). Real quotes vary with region, season, access, and scope: treat our range as a planning band, never a bid.
| Trade | SOC | Median wage (annual) | Derived hourly | Source |
|---|---|---|---|---|
| construction laborer | 47-2061 | $46,730 | $22.47/hr | BLS |
| carpenter | 47-2031 | $59,310 | $28.51/hr | BLS |
| roofer | 47-2181 | $50,970 | $24.50/hr | BLS |
| painter | 47-2141 | $48,660 | $23.39/hr | BLS |
| masonry worker group | 47-2051 proxy (masonry workers group incl. cement masons) | $56,600 | $27.21/hr | BLS |
Materials Pricing (Sampled, Not Averages)
Material figures come from a hand-sampled retail basket: named SKUs recorded manually from retail listings (big-box retail (Home Depot), Seattle-area store pricing; local prices vary), sampled 2026-08-15. We never publish a “national average” material price, because no free, legitimate source for one exists: the sites that print one are guessing, and we’d rather label a real sample honestly than dress up a fabricated number.
| Item | Unit | Sampled price |
|---|---|---|
| SAKRETE 60 lb Gray Concrete Mix | bag | $4.68 |
| SAKRETE 80 lb Gray Concrete Mix | bag | $6.24 |
| QUIKRETE 50 lb Fast-Setting Mix | bag | $7.97 |
| Rapid Set 60 lb 24/6 Fast-Setting Mix | bag | $7.97 |
| Owens Corning Oakridge Architectural Shingles (32.8 sf/bundle) | bundle | $44.97 |
| Owens Corning TruDefinition Duration (32.8 sf/bundle) | bundle | $46.97 |
| Owens Corning Starter Strip Plus (105 lin ft) | roll | $62.47 |
| 2x4x8 #2 Premium KD-HT Stud | each | $4.15 |
| 2x4x8 Premium Cut Framing Stud | each | $4.65 |
| BEHR PRO i100 Interior Eggshell (1 gal) | gallon | $24.98 |
| Vigoro 2 cu ft Shredded Mulch | bag | $3.33 |
| Earthgro 1.5 cu ft Shredded Mulch | bag | $3.97 |
| Pavestone 0.5 cu ft Paver Base | bag | $6.47 |
| Vigoro 0.5 cu ft Pea Gravel | bag | $5.97 |
| SAKRETE All-Purpose 60 lb Gravel | bag | $8.44 |
| Custom LevelQuik RS 50 lb Self-Leveling Underlayment | bag | $29.97 |
| LevelQuik 1 qt Acrylic Primer | quart | $14.97 |
Freshness
Cost data carries an as-of date (currently 2026-08-15) and our build system refuses to publish if that data ages past 120 days. If you ever see a stale date here, the refresh process has failed, so tell us.
Validation
Every calculator ships with golden-record tests validated against external authorities (NRMCA bulletins, manufacturer technical data sheets, university extension worked examples), never against other calculator websites, which copy each other’s errors. When a calculator refuses an input (a 30-inch “slab”, a structural span question), that is the validation working: outside its validated envelope, a wrong answer is worse than no answer.