Calculation Methodology & Verification
Transparent documentation of the physical conversion constants, mathematical formulas, intermediate floating-point precision, and automated test harnesses used by AutoFuelCalc.
1. Exact Physical SI Conversion Constants
All volumetric and distance transformations are executed using exact international definitions established by the National Institute of Standards and Technology (NIST) and the International System of Units (SI):
2. Derivation of Unit Conversions
A frequent error on amateur calculation websites is rounding intermediate conversion ratios (e.g. using 235.2 instead of the exact decimal fraction). At AutoFuelCalc, intermediate operations maintain IEEE 754 double-precision 64-bit floating point precision:
US MPG to L/100km derivation:L/100km = (100 × 3.785411784) ÷ (US MPG × 1.609344) = 235.214583 ÷ US MPG
US MPG to km/L derivation:km/L = (US MPG × 1.609344) ÷ 3.785411784 = US MPG × 0.425143707
3. Rounding & Display Rules
In accordance with good scientific computing practices, intermediate computations are never rounded prematurely. Values are formatted strictly upon rendering to the user interface:
- Fuel Economy (MPG, km/L, L/100km): Formatted to 2 decimal places.
- Monetary Fuel Costs: Formatted to 2 decimal places with local currency glyphs.
- Cost Per Mile / Cost Per km: Formatted to 2 or 3 decimal places to prevent truncation error over short distances.
4. Automated Regression Testing
Prior to every production deployment, automated test suites execute across 7 edge-case suites including non-zero assertions, division-by-zero traps, negative bounds, floating-point parity checks, and real-world benchmark verification against standard EPA/DOT datasets.