Electrical calculators for the NEC
Calculators for electricians working to the NEC. Each page shows its formula, a worked example and the code sections it uses, and keeps your inputs in a link you can share.
Each calculation is the method of the Electric Master app, ported to the web and tested case by case against the app’s source code. Edition: NEC 2023. Your AHJ may enforce another edition or local amendments, and it has the final word.
The App Store version of Electric Master (2.2.0) predates the NEC corrections this page follows; until its next update, its result can differ from this page for some inputs.
Wire size and ampacity
- Voltage Drop Calculator (NEC)
Volts and percent dropped on a run, single- or three-phase, and the smallest size that stays within 3 %.
- Wire Size Calculator for AC Building Wiring (NEC)
The conductor size for a load on AC building wiring, with terminal temperature, continuous loads, ambient and conductor count, and a voltage-drop check on this page.
- Wire Ampacity Chart: Copper and Aluminum (NEC Table 310.16)
Table 310.16 ampacities at 60, 75 and 90 °C: copper from 14 AWG and aluminum from 12 AWG, up to 2000 kcmil.
- Ampacity Derating Calculator (NEC)
Ampacity corrected for ambient temperature and adjusted for more than three current-carrying conductors in one raceway.
Raceways and boxes
- Conduit Fill Calculator (NEC Chapter 9)
The fill of mixed conductors in a raceway, how many more fit, and the smallest raceway that passes (Chapter 9).
- Box Fill Calculator (NEC 314.16)
The volume a box needs for its conductors, yokes, clamps, grounds and fittings (314.16), and the standard boxes that hold it.
- Conduit Bending Calculator: Offsets, Saddles and Shrink
Offsets and 3- and 4-point saddles: mark spacing, shrink and the multipliers behind them.
Grounding
- Ground Wire Size Calculator and Chart (NEC 250.122)
The equipment grounding conductor for an overcurrent device (Table 250.122), with the upsizing rule and a chart.
- Grounding Electrode Conductor Size Calculator (NEC 250.66)
The grounding electrode conductor for a service (Table 250.66), with parallel sets and the electrode limits.
The Electric Master app for iPhone and iPad has 20 NEC calculators and a panel planner, works offline, and covers the Canadian Electrical Code as well.
About the app