Methodology

This page explains how the RenovationCalcs calculators are derived and verified — and why they need no ongoing maintenance to stay correct.

1. Timeless math, stable conventions

Every tool computes from a closed-form formula: area = length × width; wall area = perimeter × height − openings; material quantity = area ÷ coverage × (1 + waste); project cost = quantity × your unit price + labor; price per sq ft = your total ÷ area; loan payment = P·r ÷ (1 − (1+r)⁻ⁿ). The only baked-in numbers are stable conventions — a 4×8 drywall sheet is 32 sq ft; paint covers ~350–400 sq ft per gallon per coat; tile and flooring waste is about 10–15%. These do not drift, so the statements stay true over time.

2. No prices, no feeds

There is deliberately no material price, no labor-rate table, no regional cost index, no live loan rate and no product catalog. Every cost tool works on the prices you enter from your own quotes and bills ($/sq ft, $/gallon, $/sheet, $/linear ft, per-unit price, labor $/hour, APR). That is why the site is correct regardless of what materials, labor or interest rates do.

3. Numeric self-check

Every formula is asserted against a worked example with known numbers (for instance: a 12×15 room has ≈ 396 sq ft of wall → 3 gallons at two coats; 612 sq ft ÷ 32 = 20 drywall sheets; a 1,800 sq ft renovation at $75/sq ft is $135,000; $30,000 at 8% over 60 months is ≈ $608.29/month). A release gate runs all of these and fails on any mismatch, so "verification" here is mathematical correctness plus accurate conventions — not a time-based check.

4. Estimate, not a bid or a load of engineering

The coverage, waste and allocation values are labeled planning bands — a starting point, not a spec sheet, and the cost-per-sq-ft bands are explicitly not a price index. Every cost result is a planning estimate: get itemized written quotes from licensed contractors, and treat structural, electrical, plumbing and gas scope as licensed-pro, permit-and-inspection work. The financing and ROI tools are illustrative math on your figures, not financial advice, and added resale value is never guaranteed.