Electrical Calculators

Five electrical calculators built on the US National Electrical Code (NEC). Size conductors and check ampacity against NEC 310.16 with temperature and conduit-fill derating, keep voltage drop within the recommended 3% on a branch circuit and 5% overall, count box fill per NEC 314.16, check raceway fill per NEC Chapter 9, and run a dwelling service-load calculation per NEC Article 220. Every calculation runs locally in your browser, with nothing uploaded.

These calculators serve electricians, estimators, and electrical engineers who need fast, code-referenced answers during design and rough-in. Correct conductor sizing balances ampacity — set by NEC Table 310.16 and reduced by ambient temperature and the number of conductors in a raceway — against voltage drop, which the NEC recommends keeping under 3% on a branch circuit and 5% from the service to the outlet. Undersized conductors overheat and waste energy; oversized ones add needless cost and are harder to terminate.

Box and conduit fill are among the most common inspection failures. NEC 314.16 sets the minimum cubic-inch volume required per conductor in outlet and device boxes, while NEC Chapter 9 limits raceway fill to 40% for three or more conductors. The Dwelling Load Calculator follows the NEC Article 220 standard method to size a home's electrical service. Each tool works on its own, and together they cover the everyday residential electrical math from the service entrance to the device box. Results are for preliminary design and should be verified against the code edition your jurisdiction has adopted.