Methodology

Each tool separates its numeric engine from display formatting. Length is converted to metres before geometric calculations. Area and volume are converted using exact definitions: 1 foot = 0.3048 metres, 1 inch = 0.0254 metres, and 1 yard = 0.9144 metres.

Rounding and purchase quantities

Intermediate calculations retain JavaScript floating-point precision. Display values are rounded, generally to two decimals. Bags, packs, tiles and whole sales units round upward. Currency display does not convert exchange rates; choose one currency consistently. Invoice tax is calculated once after discount, then formatted; local tax rounding rules may differ.

Finance and energy models

Mortgage calculations use a fixed nominal annual rate divided by payment frequency. Compound growth uses an equivalent contribution-period rate. Solar uses owner-entered generation and tariffs. Cooling is explicitly a simplified heuristic. Tool pages document details rather than implying these models apply universally.

Verification and corrections

Known-answer fixtures, zero-rate cases, unit conversions, invalid inputs and numeric regressions protect engines. These tests establish the documented mathematics, not a professional certification. Last reviewed: 2026-10-07.

Reference definitions

NIST unit definitions and SI usage support conversion constants. Material coverage and yields must come from the product supplier. No live tariffs, financial rates or weather data are fetched.