Conduit Fill Calculator is a small set of free, fast electrical calculators for electricians, apprentices, estimators, engineers and serious DIYers. Each tool does one job well and shows its working, so you can see exactly which code table a number came from.
What we offer
- Conduit Fill Calculator — Check NEC Chapter 9 fill for any mix of wires in EMT, PVC, rigid, IMC, ENT, FMC or LFMC.
- Wire Size Calculator — Find the right AWG/kcmil for a load using Table 310.16, derating and voltage drop.
- Voltage Drop Calculator — Voltage drop for single-phase, three-phase and DC circuits in copper or aluminum.
- Ampacity Calculator — Allowable ampacity with ambient temperature correction and conductor bundling adjustment.
- Box Fill Calculator — NEC 314.16 box fill: conductors, clamps, devices and grounds vs. box volume.
Where the numbers come from
Our calculations use published values from NFPA 70, the National Electrical Code: Chapter 9 Tables 1, 4, 5, 5A and 8 for raceway fill and resistance; Table 310.16 with Tables 310.15(B)(1) and 310.15(C)(1) for ampacity; and Section 314.16 for box fill. Results for the conduit fill calculator are tested against the published counts in Informative Annex C.
Our approach
We keep pages light so they load quickly on a phone at the job site, we don't require sign-ups, and we explain the formula behind every result. If you spot an error, please let us know — accuracy matters more to us than anything else.
These tools support, but do not replace, the code book and the judgment of a qualified electrician. See our disclaimer.