Wire Size Calculator
Calculate the correct wire gauge per NEC 2023 Table 310.16. Includes ampacity derating, voltage drop, breaker sizing, and equipment grounding conductor for residential, solar, marine, and industrial applications.
Home wiring per NEC 310.16 at 60°C
How This Calculator Works
This tool sizes electrical conductors using the NEC 2023 (NFPA 70) ampacity tables and voltage drop formulas. It applies three NEC derating factors to find the smallest wire that safely carries your load:
- Ampacity (NEC Table 310.16) — Base current capacity at 60°C, 75°C, or 90°C for copper and aluminum conductors from 14 AWG to 500 kcmil.
- Ambient Temperature Correction (NEC 310.15(B)(1)) — Reduces ampacity when ambient temperature exceeds the 30°C base.
- Conduit Fill Adjustment (NEC 310.15(C)(1)) — Reduces ampacity when more than 3 current-carrying conductors share a raceway.
After finding the wire that meets ampacity, it checks voltage drop using the formula: Vdrop = I x R x L x factor, where factor is 2 for single-phase and sqrt(3) for three-phase. If voltage drop exceeds your limit, the wire is upsized.
Solar Mode (NEC 690.8)
When Solar / PV mode is selected, the calculator applies the NEC 690.8 solar factor of 1.56x (1.25 for irradiance x 1.25 for continuous load) to the short-circuit current (Isc) before sizing the conductor and breaker.
NEC References
- NEC 2023 Table 310.16 — Ampacity of insulated conductors
- NEC 310.15(B)(1) — Ambient temperature correction
- NEC 310.15(C)(1) — Conduit fill adjustment
- NEC 240.6(A) — Standard breaker sizes
- NEC 250.122 — Equipment grounding conductor sizing
- NEC 690.8 — Solar PV conductor sizing
- NEC 110.14(C) — Temperature limitations at terminals
- ABYC E-11 — Marine electrical standards
Disclaimer
This calculator is for reference only. Always verify results with the current edition of the NEC and consult a licensed electrician for your specific installation. Local codes may impose additional requirements beyond the NEC.