NEC Calc Pro

Seven electrical calculators that work with no signal, for electricians, apprentices and inspectors who need an answer on site rather than a search result.

WHAT IT CALCULATES

• Voltage Drop — AC and DC, single and three phase
• Wire Size — ampacity with derating for temperature and conduit fill
• Conduit Fill — percentage fill and jam ratio, eight raceway types
• Box Fill — volume and conductor allowances
• Breaker / OCPD — standard device sizes and their limits
• Motors — full-load current and branch circuit device sizing
• Ohm's Wheel — volts, amps, watts, ohms

THREE CODE EDITIONS, SWITCHABLE IN TWO TAPS

NEC 2020, 2023 and 2026 all ship. This matters more than it sounds: the answers change between editions, and so do the table numbers cited. The box-fill volume table alone is numbered three different ways across those three cycles.

The app never tells you which edition your jurisdiction has adopted. It cannot know that, and being wrong about it would be worse than being silent.

EVERY RESULT NAMES ITS SOURCE

Each answer carries the article and table it came from, and the rule that bound it — not just the number. When a wire size is capped by a termination temperature rather than by ampacity, the result says so. You can check the work, and so can an inspector.

WORKS WITH NO SIGNAL

Everything runs on the device. No account, no sign-in, no connection. The basement, the new build and the parking garage are where this gets used.

WHAT YOU PAY, ONCE

Voltage Drop, Wire Size and Ohm's Wheel are free permanently — not a trial.

A single one-time purchase unlocks Conduit Fill, Box Fill, Breaker / OCPD and Motors. There is no subscription, there are no ads, and nothing about you is for sale. That only works if the people using the app are the ones paying for it.

PRIVACY

Nothing you enter leaves this device. No account, no advertising and no usage tracking. If the app crashes, a technical report is sent to help fix the fault; it carries the error, the device model and the OS version, and never what you typed.

HOW THE NUMBERS WERE BUILT

Every table was verified three ways before it shipped: an independent transcription, a second reading against the published source, and a worked example from outside this project. Where a discrepancy turned up, it was investigated rather than smoothed over, and the findings are published. If a number ever looks wrong, send the inputs and the edition and you will get a real answer.

Calculation aid — not a substitute for the National Electrical Code or for the authority having jurisdiction. Results are provided for reference by qualified professionals and are not a substitute for the adopted electrical code, engineering judgment, or the requirements of the Authority Having Jurisdiction. Verify all results against the code edition legally in force at
your location. Use at your own risk; no warranty of fitness for a particular purpose.

This app reproduces no code text. It carries independently derived numeric values and article references, and every result names the article it came from.

NEC® and National Electrical Code® are registered trademarks of the National Fire Protection Association. This app references them nominatively to identify the code it calculates against. It is not affiliated with, endorsed by, or sponsored by NFPA.