Free · NEC 2020 · No signup
NEC electrical calculators
built for the field
Voltage drop, wire sizing, ampacity, and conduit fill — every result cites the NEC table and article. Verified against Southwire. Works on your phone on the jobsite.
- Cited to the NEC
- Table number and edition stated for every result. Default NEC 2020.
- Verified against Southwire
- Reference scenarios checked within 1% of Southwire's calculator before any tool ships.
- Jobsite-ready
- Fast on any phone. No account, no email capture, no popups.
Calculators
Voltage Drop
AC and DC voltage drop calculations, NEC Chapter 9 resistance data.
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Voltage Drop Calculator
Single- and three-phase AC drop. K-factor under #2 AWG, NEC Table 9 for #2 and larger. Flags the 3% and 5% NEC recommendations.
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DC Voltage Drop Calculator
DC circuits — solar, battery banks, marine — using NEC Chapter 9, Table 8 resistance values.
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3-Phase Voltage Drop Calculator
Three-phase voltage drop using the √3 multiplier. NEC Table 9 AC resistance, same method as the main VD tool.
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12V Voltage Drop Calculator
Automotive, RV, and battery systems. Defaults to 12V; override for 24V and 48V banks.
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Extension Cord Voltage Drop
Match a cord gauge (16–10 AWG) to a tool load. Practical 3% guideline; K-factor method.
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Wire & Conductor Sizing
Size conductors per NEC Table 310.16 with derating and voltage drop cross-checks.
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Wire Size Calculator
Returns the minimum conductor for a load, distance, and target voltage drop. Checks NEC Table 310.16 ampacity, derating, and standard OCPD sizes.
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Wire Gauge Calculator
Enter a required ampacity, get the minimum AWG. NEC Table 310.16 with full derating — ambient, conductor count, and 110.14(C) termination cap.
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Wire Ampacity Calculator
Derated ampacity per NEC 310.15 — ambient correction, conductor-count adjustment, and 110.14(C) termination cap.
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Conduit Fill
NEC Chapter 9 Table 1 fill limits and Annex C conductor counts.
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Conduit Fill Calculator
Mixed conductors in EMT, RMC, IMC, or PVC against the 53% / 31% / 40% limits in NEC Chapter 9, Table 1.
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Conduit Size Calculator
Minimum conduit trade size for your conductor bundle across EMT, RMC, IMC, and PVC Schedule 40/80 — all in one comparison table.
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EMT Conduit Fill Calculator
Fill calculation locked to EMT. Minimum trade size and actual fill percentage for your conductor bundle.
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PVC Conduit Fill Calculator
PVC Schedule 40 and Schedule 80 fill per NEC Chapter 9. Separate Table 4 areas applied for each schedule.
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Conduit Fill Table
Max same-size conductor counts from NEC 2020 Annex C — EMT, IMC, RMC, PVC Sch 40/80. THHN/THWN-2 and XHHW-2. Printable.
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