Voltkit: NEC Conduit Fill Calc

Voltkit is a precision NEC calculator built for working electricians — fast, accurate, and 100% offline. Every result cites the exact NEC 2023 table or formula behind it, so you can trust the number on the job and back it up to an inspector.

— 21 PRO CALCULATORS —
• Voltage Drop — approximate-K and exact Chapter 9 (Table 9 R/X) methods
• Conduit Fill — 10 raceways and every insulation, Chapter 9 Table 4, with the Note 7 same-size round-up
• Wire Size — the smallest conductor that meets ampacity, voltage drop and the 240.4(D) small-conductor limits, with an optional 310.12 dwelling-service rule
• Wire Ampacity — Table 310.16 with ambient and bundling adjustments, plus free-air
• Box Fill — NEC 314.16 with a full standard-box picker, per-device yoke sizing and the quarter allowance for each EGC past four
• Conduit Bending — 90° stub-up, offset, rolling, and saddle, with a scaled bend diagram
• Bend Length, Segment Bend, Bend Total, and Concentric — a full pipe-bending suite
• Ohm's Law and AC Power — watts, VA, and power factor, single- and three-phase
• Grounding — EGC (250.122), GEC (250.66), and 250.122(B) upsizing
• Dwelling Load — optional and standard methods (Article 220)
• Motor — full-load current, conductor, overload, and OCPD (Article 430)
• Plus Transformer, Pull Box, Parallel Sets, Motor Feeder, Power-Factor correction, and Appliance Demand

— BUILT FOR THE FIELD —
• Works entirely offline — every NEC table lives on your device, no signal required
• Show Calculation — open any result into clear, step-by-step math
• Save jobs and reopen them later from your calculation history
• Built-in NEC reference tables: ampacity, conduit fill, box fill, conductor properties, and more
• NEMA receptacle and conductor color-code references

— WHY ELECTRICIANS TRUST VOLTKIT —
Every calculation is derived from a published NEC 2023 table or formula and checked against authoritative worked examples (Mike Holt, Ugly's, NEC Annex C). No ads, no clutter, no internet required — just a clean, precise instrument that respects your trade.

— FREE, WITH OPTIONAL PRO —
Voltkit is free to use: every calculator gives you a complete, NEC-cited result and full worked steps. Voltkit Pro unlocks the advanced options for commercial and industrial work — three-phase, exact-impedance voltage drop, free-air ampacity, every raceway and insulation, larger conduit, box and parallel runs, over-1000 V transformers, and the full standard load calc — plus unlimited saved calculations. Prices may vary by region.

Built in the US for NEC 2023. Canadian CEC, BS 7671, and AS/NZS 3000 code packs are on the roadmap.

Voltkit is an independent tool and is not affiliated with or endorsed by the NFPA.

Recent changes:
• Conduit Fill: Chapter 9 Note 7 round-up for same-size wires, so 22 #14 THHN in 3/4" EMT now reads OK, as in Annex C.
• Box Fill: each device yoke is sized by the largest wire on that device (314.16(B)(4)); studs and hickeys count once per type; each EGC past four adds ¼ (314.16(B)(5)). The old version could under-count a box with 5+ grounds.
• Wire Size: 240.4(D) small-conductor limits, plus an optional 310.12 83% rule for dwelling services.
• Support: hello@voltkitapp.com