Electrical Calculators
Electrical wire sizing involves two independent constraints: ampacity (the wire's current-carrying capacity) and voltage drop (signal loss over distance). Both must be satisfied — the larger wire wins. Our tools use the NEC circular mil method and resistance tables from Chapter 9, Table 8.
These calculators are for estimation and educational purposes. Always verify results with a licensed electrician and your local building codes. Undersized wiring is a fire hazard — when in doubt, go one gauge larger.
All Electrical Tools
Key NEC References
- Max voltage drop (branch): 3% recommended (NEC 210.19 FPN)
- Max voltage drop (total): 5% combined feeder + branch
- K factor (copper, 75°C): 12.9 ohms·cmil/ft
- K factor (aluminum, 75°C): 21.2 ohms·cmil/ft
- Minimum residential wire: 14 AWG for 15A circuits, 12 AWG for 20A
Safety Disclaimer
Electrical work requires permits and inspections in most jurisdictions. These calculators help you understand wire sizing requirements but do not replace professional electrical design. Factors like ambient temperature, conduit fill, and continuous loads require additional derating not covered by these simplified tools.