Sources

The formulas and constants behind the calculators come from physics, conductor geometry and recognized engineering standards:

• AWG wire geometry and resistance (circular mils, ohms per 1,000 ft): ASTM B258 and NEC Chapter 9, Table 8.
• Conductor ampacity: NEC Table 310.16 (60/75/90°C, copper and aluminum), with temperature and conductor-bundling adjustment factors per NEC 310.15.
• Conduit cross-sections and the 40% fill rule, plus THHN/THWN conductor areas: NEC Chapter 9, Tables 1, 4 and 5.
• Copper and aluminum resistivity (the K factor in cmil·Ω/ft) used in the voltage-drop and resistance formulas: standard engineering values.
• Peak sun hours by US state: NREL geographic averages (a stable design figure, not a live feed).
• Typical appliance running and starting watts: manufacturer nameplate ranges (read your own nameplate for an exact value).

NEC values reference the stated edition (NEC 310.16 / Chapter 9, ed. 2020/2023) — confirm the edition adopted by your jurisdiction. The cost tools contain no electricity tariffs: you enter $/kWh, $/gal and other rates yourself, so the site stays correct with no maintenance.