The National Electrical Code is organized by chapter, article, section, and table. If you already know the section number you need, this page jumps you straight to the calculator that implements it. If you do not, the plain-English column tells you what each section is for.
All calculators here are free, run entirely in your browser, and print the NEC reference next to every result so you can show your work to an inspector or a senior journeyman.
Conductor sizing & ampacity
| NEC reference | What it covers | Calculator |
|---|---|---|
| Table 310.16 | Allowable ampacity of insulated conductors at 60, 75, 90 deg C in raceway, cable, or earth. | NEC Wire Size Calculator |
| 210.19(A) / Chapter 9 Table 9 | Branch-circuit voltage drop guidance (3% branch / 5% total) and per-foot conductor resistance. | Voltage Drop Calculator |
| Article 220 (standard method) | Residential service load calculation by general lighting, small-appliance, laundry, fastened-in-place, and largest-of fixed appliance loads. | Electrical Load Calculator |
Raceway & box fill
| NEC reference | What it covers | Calculator |
|---|---|---|
| Chapter 9 Table 1 | Maximum percent fill in a conduit: 53% for one conductor, 31% for two, 40% for three or more. | Conduit Fill Calculator |
| Chapter 9 Table 4 | Conduit interior cross-sectional area at 100% fill, by raceway type and trade size. | Conduit Fill Calculator |
| Chapter 9 Table 5 | Approximate area of insulated conductors (THHN, XHHW, RHH, etc.) by AWG / kcmil. | Conduit Fill Calculator |
| 314.16(A) | Cubic-inch capacity of standard metal outlet, device, and pull boxes. | Box Fill Calculator |
| 314.16(B) | Volume allowance per conductor (14 AWG = 2.00 cu in, 12 = 2.25, 10 = 2.50, 8 = 3.00, 6 = 5.00). | Box Fill Calculator |
Grounding & bonding
| NEC reference | What it covers | Calculator |
|---|---|---|
| Table 250.66 | Grounding electrode conductor (GEC) size based on the largest ungrounded service-entrance conductor. | Grounding Conductor Sizer |
| Table 250.122 | Equipment grounding conductor (EGC) size based on the rating of the branch-circuit overcurrent device. | Grounding Conductor Sizer |
| 250.122(B) | EGC must be increased proportionally when the phase conductors are upsized for voltage drop. Recompute by hand if you upsized. | Grounding Conductor Sizer + Wire Size |
Motors
| NEC reference | What it covers | Calculator |
|---|---|---|
| 430.6(A)(1) | Use the FLA from NEC Tables 430.247-250 for sizing conductors and OCPD – not the motor nameplate. | Motor FLA Calculator |
| Tables 430.247-250 | Full-load current of DC, single-phase, two-phase, and three-phase AC motors by horsepower and voltage. | Motor FLA Calculator |
| 430.22 | Branch-circuit conductors for a single continuous-duty motor: 125% of motor FLA. | Motor FLA Calculator |
| Table 430.52 | Maximum branch-circuit OCPD: 250% (inverse-time breaker), 175% (time-delay fuse), 300% (non-time-delay fuse), 800% (instantaneous-trip breaker). | Motor FLA Calculator |
| 240.6(A) | Standard ampere ratings for fuses and inverse-time breakers (15, 20, 25, … 1200 A and beyond). Used to round OCPD up. | Motor FLA Calculator |
| 430.110 | Disconnect ampacity rating for a motor: not less than 115% of FLA. | Motor FLA Calculator |
How to read a code citation
NEC citations look like Table 250.66 or 430.22(A)(1). Read them as:
- Article – the three-digit prefix (250 = Grounding and Bonding, 310 = Conductors, 314 = Outlet boxes, 430 = Motors).
- Section – the two-digit suffix after the dot (250.66 = the GEC sizing table inside Article 250).
- Subdivision – the parenthesized letters and numbers ((A)(1) = “first item under subsection A”). Subdivisions almost always carry the exception or the upper limit you actually need.
The Chapter 9 tables are different – they sit at the back of the code and are referenced by raceway sizing, conduit fill, and conductor properties. They are tables of numbers without an article number.
Reading the actual NEC text
This hub maps citations to calculators, but sometimes you need to read the code itself. The NFPA hosts a free, official, read-only version of the current NEC on their portal (account required, no payment). See How to Read the NEC Codebook Online (Free, Legally) for the link, what the NFPA Handbook adds over the free code, and which sections to read first.
Things this hub deliberately does not cover
- Hazardous (Classified) Locations – Article 500. The classification work happens before any of these calculators apply. Hire a qualified PE for Class 1 / Class 2 / Class 3 designs.
- Health Care Facilities – Article 517. Special isolated power systems and redundant grounding rules. Not covered.
- Photovoltaic and Energy Storage – Article 690 / 706. The Solar Payback Calculator is a financial estimator, not a 690 design tool.
- Communications Cabling – Chapter 8. Different ampacity tables, different separation rules. Not covered.
Suggest a calculator
If a section you reach for often is missing from this hub, open an issue on the project repository or use the contact page. The shortlist for upcoming additions: voltage drop for three-phase commercial feeders, generator sizing, EV charger circuit design, and Manual J-lite HVAC sizing.
Calculators are for planning and estimating only. They are not a substitute for a stamped engineering design or a permitted electrical drawing. When in doubt, hire the appropriate licensed professional.
