Wire Size Calculator

SolversPro Wire Size Calculator is a free electrical engineering tool that computes the required American Wire Gauge (AWG) conductor diameter and circuit voltage drop based on current load, cable length, system voltage, and metal resistivity.

NEC Conductor Ampacity & Cross-Section Reference

Standard NEC 310.16 conductor ratings for copper and aluminum conductors rated at 75°C (THHN/THWN-2):

AWG / kcmil Size	Circular Mils (CM)	Copper (Cu) 75°C	Aluminum (Al) 75°C	Typical Standard Circuit
14 AWG	4,110 CM	15 A	Not Permitted	15A general lighting and convenience receptacles
12 AWG	6,530 CM	20 A	15 A	20A kitchen/bath small appliance circuits
10 AWG	10,380 CM	30 A	25 A	30A electric water heaters and dryer feeds
8 AWG	16,510 CM	50 A	40 A	Electric ranges and central A/C compressors
6 AWG	26,240 CM	65 A	50 A	50A EV fast chargers and subpanel feeders

Frequently Asked Questions

/What is Voltage Drop?

Voltage drop is the decrease of electrical potential along the path of a current flowing in an electrical circuit. The National Electrical Code (NEC) recommends a maximum voltage drop of 3% for branch circuits to ensure equipment operates efficiently.

/Why does wire material matter?

Different materials have different resistivity (K). Copper is a better conductor (K=12.9) than aluminum (K=21.2), meaning you generally need a thicker aluminum wire to carry the same current over the same distance as copper.

/How is this calculated?

We use the standard industry formula: Circular Mils = (K × I × L × Phase Factor) / Allowable Voltage Drop. The result is then mapped to the next largest standard AWG or kcmil wire size.

/What is the difference between single-phase and three-phase circuit calculations?

Single-phase circuits utilize a phase factor of 2 to account for both out-and-back conductor runs, whereas balanced three-phase calculations utilize the square root of 3 (√3 ≈ 1.732) line-to-line factor.