Methodology & Sources

This page explains how our calculators are built, what sources the numbers come from, and where our estimates stop being reliable. If you ever want to check our work, start here.

1. Code-derived figures

Where a calculator enforces a limit, that limit comes from the International Residential Code (IRC) and is cited on the page:

• Stair geometry — maximum riser height and minimum tread depth per IRC R311.7.
• Baluster / guard spacing — the 4-inch sphere rule per IRC R312.
• Attic ventilation — the 1:150 and 1:300 net free area ratios per IRC R806.
• Frost depth — regional footing depth tables; these are set locally and must be confirmed with your building department.

Important: jurisdictions amend the model code and adopt different code cycles. Our figures reflect the model IRC. Your local code governs.

2. Manufacturer specifications

Yields and coverage rates come from current product datasheets, not estimates:

• Concrete bag yields — 0.45 cu ft per 60 lb bag and 0.60 cu ft per 80 lb bag, per Quikrete and Sakrete published yields.
• Paint spread rate — approximately 350–400 sq ft per gallon on primed drywall, per major manufacturer datasheets. Porous, textured, or unprimed surfaces consume substantially more.
• Insulation R-values — per-inch values from fiberglass, mineral wool, and foam board manufacturer literature.
• Epoxy pour depth — maximum single-lift depths from deep-pour resin manufacturers, which vary by product and exotherm behaviour.

Manufacturers revise these figures. Where your product's bag or datasheet disagrees with our default, use the product's number.

3. Waste factors

Waste allowances are industry-standard ranges for the material and installation pattern, and every calculator exposes the waste factor as an editable input so you can override it:

• Straight-lay flooring and tile: 10%
• Diagonal or herringbone patterns: 15–20%
• Concrete: 5–10% for over-excavation and subgrade irregularity
• Roofing: 10%, higher on cut-up roofs with multiple valleys and penetrations

These are planning allowances, not guarantees. Complex layouts, out-of-square rooms, and material defects can push actual waste higher.

4. Pricing data

• Material prices reflect national-average retail pricing at major home-improvement retailers at the time the page was last reviewed.
• Labor rates reflect typical national-average professional installation rates by trade.

Pricing is the fastest-decaying data on this site. Regional variation is large, and material costs have been volatile. Treat every cost output as an order-of-magnitude planning figure and get a local quote before committing.

5. What we do not do

We think it is more useful to be clear about the boundary than to overstate the tools:

• We do not perform structural engineering. Beam sizing, truss design, load paths, and footings carrying structural load require a licensed engineer. Our beam and truss tools calculate material quantities once you already know the required size — they do not tell you what size to use.
• We do not account for local code amendments, snow and wind loads, seismic zones, or soil conditions.
• We do not provide quotes. Nothing on this site is a bid or a binding estimate.
• We do not inspect your project. A calculator cannot see that your room is out of square or your subgrade is soft.

6. Corrections

If a number here is wrong or has gone stale, we want to know. Reports go to the Contact Page; corrections are made and the page's review date is updated. We would rather be corrected than confidently wrong.

7. How this site is made

JusTheTool is a small independent project, built with the assistance of AI tooling and maintained by its owner. We do not claim a staff of tradespeople. What we do claim is that every constant above is traceable to a published source you can check yourself — which we think is a more useful thing to offer than an assertion of authority.