Where every number on this site actually comes from.
Every number on this site comes from one of three places: the manufacturer’s data sheet for the bag I’m holding, the practice guidance from the trade body that publishes it, or what I learned the expensive way on a flip. The order of the tiers is also the order of trust.
Manufacturer spec sheets first — because the Quikrete bag tells you what’s in the bag, and the Daltile box tells you the coverage in square feet. Trade-body guidance second — because the American Concrete Institute has watched more pours than I will in a lifetime, and the TCNA waste percentages are based on decades of installation data. Lived experience third — not as the primary citation, but as the marginalia that explains why the published number doesn’t survive contact with a Saturday in July.
- 01Manufacturer data sheetsBagged products, ready-mix design specs, fastener load tables.Quikrete 80 lb concrete mix yields 0.6 ft³ per bag per the printed spec on the bag. Ozinga ready-mix is sold by the cubic yard with a published 3 yd³ minimum for residential delivery in Cook County. Daltile / MSI box coverage and waste-factor norms come from the manufacturer install guides. Numbers traceable to a printable PDF or a bag in the garage.
- 02Trade-body practice guidanceACI, NRMCA, TCNA, NDS, ICC residential code.The 4-inch residential slab thickness, the 5% waste cushion default, the deck-footing depth-by-frost-line table — sourced to ACI 332 residential concrete practice, the TCNA Handbook for tile waste percentages, IRC R403 for footings, and AWC DCA-6 for prescriptive deck framing. Citations sit inline on each calculator’s methodology drop-down.
- 03Lived experience — the expensive lessonsMarginalia, not citation. Always labelled as such.The order-cushion sizing, the bagged-vs-ready-mix inflection point around 1.5 yd³, the “don’t order short” default — these come from three Chicago-area flips and are labelled as field notes throughout the site. Read them as the operator’s opinion, not as published guidance.
- 04What is never the sourceThe provenance line we draw a hard line on.No competitor calculator outputs are reverse-engineered. No forum posts are paraphrased as fact. No Amazon product copy is used as a spec source. Pinterest landscape content is not a citation. If a number can’t be tied to a manufacturer sheet, a trade body, or a flip I personally ran, the calculator doesn’t ship the number.
Per-calculator sourcing
Sources are layered by what kind of claim they back, not flat-listed. ACI 318 is structural code, not yardage arithmetic — citing it for “how many yards do I order” reads as miscalibrated authority.
| Cluster | Geometry | Yields & coverage | Practice + waste | Code |
|---|---|---|---|---|
| Concrete | Site arithmetic (own derivation, formula shown) | Quikrete / Sakrete / SpecMix bag-yield data sheets | NRMCA + manufacturer (waste %, delivery minimums, slump) | ACI 318, IRC 2021 (only for structural concrete) |
| Topsoil | Site arithmetic | Bag-volume conventions per supplier (40 lb / 1 cu ft typical) | USDA NRCS bulletins; cooperative-extension services | — |
| Mulch | Site arithmetic | Bag conventions (2 cu ft / 3 cu ft) | Cooperative extension; ANSI A300 for depth recommendations | — |
| Tile | Site arithmetic + manufacturer box-coverage data sheets | Manufacturer waste norms (10% standard, 15% diagonal/herringbone) | Manufacturer install guides | TCNA handbook, ANSI A108 / A118 (for installation method content) |
| Deck (v1 surface-only) | Site arithmetic | Manufacturer span tables for board count per linear foot | Manufacturer install + fastener guidance | AWC DCA-6, IRC 2021 Ch.5 (only when guides touch structural) |
| Gravel (driveway / walkway / drainage / decorative) | Site arithmetic + per-type loose density (pea 96 / clean 100 / crusher run 115 / decorative 95 lb/ft³) | Supplier spec sheets (Vulcan Materials, Lehigh Hanson, regional Chicago-metro yards) cross-checked against Omnicalculator + InchCalculator ranges | Compaction guidance (15-20% loose-to-compacted on crusher run); Chicago-metro supplier minimums (5 yd³ typical) | USDA NRCS TN 210-AEN-04 + NRCS Construction Spec 495 (Geotextile), Spec 423 (Earthfill and Gravel Fill) — when methodology touches driveway-base prep |
| Electrical (rewire / panel / service / partial) | Site arithmetic (own derivation, formula shown) | Square D / Eaton / Siemens / GE / Leviton panel + breaker spec sheets | NECA labor units (where citable); Chicago-metro permit fee schedules; manufacturer install guides | NEC / NFPA 70 §210.12 (AFCI), §210.8 (GFCI), §230 (service entrance), §250 (grounding), §408 (panels), §314 (box fill), §110.26 (working space) |
| Plumbing (repipe / main line / branch / galv-to-PEX / repair) | Site arithmetic (own derivation, formula shown) | Uponor / SharkBite / Apollo PEX A/B install guides; Mueller copper Type L/M spec sheets; CPVC + cast iron manufacturer specs | MCAA (Mechanical Contractors Association) labor units where citable; Chicago-metro plumbing permit fee schedules; per-mode supplier minimums | UPC 2024 §604 (water distribution), §605 (PEX install), §609 (drain pipe); IPC 2024 §312 (system pressure testing), §605 (backflow protection). Lead-free-solder remediation anchored on Safe Drinking Water Act 1986 + EPA Lead and Copper Rule (LCRR), NOT IPC 312. |
Project-level cost methodology — what’s anchored, what’s a planning range
The project-planning group (gut-rehab cost calculator, construction timeline calculator) outputs SiteworkMath planning ranges, not contractor bids or schedules. The distinction matters: a planning range is the dollar number or calendar window an operator uses to decide walk / bid / kill before paying for inspections and a contractor walk-through. A bid is what the GC commits to once the property has been walked, the leak-check flags resolved, and the line items scoped to specifications. They’re different documents with different evidentiary standards.
Three sources sit underneath the project-planning numbers:
- Anchored — Census 2024 Survey of Construction for the owner-builder slowdown (15.2mo OB / 12.1mo contractor → 1.26x), and Assembly Service IL Chicago for the $100–300/sqft gut-rehab band cited verbatim. These two sources do real work in the engine and get cited in every output.
- Sanity-checked — NAHB’s 2024 construction-cost survey and its 8-stage cost breakdown are sanity checks, not constructive multipliers. The 16.7% NAHB profit + overhead figure is on SALE PRICE, a different calculation that includes builder profit on the resale. SiteworkMath’s GC overhead line uses 10–15% on hard costs (mid 12.5%), which reflects Chicago-metro residential GC industry typical and is the correct calculation for a feasibility budget.
- Calibrated — Phase durations and per-line dollar baselines are SiteworkMath calibrations from flipper experience plus HomeAdvisor, Fixr, and Angi cost-guide cross-checks plus AIA A201 contract cadence patterns. These are planning ranges, never published as point estimates. Confidence labels (high / medium / rough) and Rehab Leak Check sensitivities make the uncertainty visible rather than hiding it behind a single number.
The Budget Cushion (cost calc) and Schedule Cushion (timeline calc) are the project-level analogs of the Material Order Cushion. Same 4-line moat pattern: the math, the practical floor, why the cushion exists, and when not to over-pad. They are the operator-facing signal that a feasibility budget and a contractor bid are different documents with different uses.
Gut rehab vs new construction — what differs
Both project-planning cost calculators run the same engine. They differ in three places. Line catalog: new-build adds a site-prep phase where rehab has demo; new-build always includes foundation where rehab leaves it optional; new-build framing + envelope baselines reflect full-scope work from scratch instead of partial repair. Per-sqft baselines: new-build standard 2000 sqft default lands at ~$157/sqft mid, just below the NAHB 2024 $162.50/sqft average; gut-rehab default lands at ~$144/sqft because foundation is opt-in and framing is repair not new. Rehab Leak Check:rehab surfaces 7 property-specific risk-flag inputs that modulate contingency; new-build hides those flags because there’s no existing structure to leak — the strict-permit-jurisdiction risk is captured in the input row instead. NAHB 2024 $162.50/sqft is a cross-check anchor, not a constructive multiplier.
Why every output ends with four lines
Every calculator on the site outputs a Material Order Cushion: the exact math, the practical order, why the cushion exists, and when not to over-order. The math line is the geometric answer. The practical line is what I’d call the supplier with. The cushion explanation is the marginalia I wish someone had handed me on the first slab. The ceiling caveat is the part that keeps you from ordering a yard of ready-mix you can’t legally buy below the plant minimum.
Other calculators ship line one. The other three are the difference between knowing the answer and knowing the order.
What we don’t do
We don’t fabricate hobbyist anecdotes. We don’t cite publication numbers we haven’t verified — UC ANR / MSU Extension bulletins are a known LLM-confabulation hazard and every cite goes through a verify-before-write check. We don’t present AI-generated images as photographs. When a calculation has known uncertainty, we state it conservatively rather than rounding optimistically.
Questions or corrections? Contact us.