Wire Size Calculator
Calculate optimum AWG and kcmil conductor sizes for AC single-phase, three-phase, and DC circuits. Evaluates both thermal ampacity and voltage drop limits.
Circuit Parameters
Recommended Conductor Gauge
Optimal gauge satisfying voltage drop and NEC rules
8 AWG 8.37 mm²
Actual Voltage Drop 3.12 V (2.60%)
Voltage at Load 116.88 V
Resistance 0.078 Ω
Power Loss 62.4 W
Wire Sizing Formulas
The governing wire size is the larger of the gauge needed to safely carry continuous current without overheating (NEC 310.16) and the gauge needed to restrict voltage drop to within acceptable operational thresholds (NEC 210.19(A) Informational Note 4).
Formula:
1Ø CM = (2 × K × I × L) / V_drop | 3Ø CM = (1.732 × K × I × L) / V_drop | Wire Size = max(AWG_ampacity, AWG_vdrop) Variables & Parameters
CM Required conductor cross-sectional area in Circular Mils
K Specific wire resistance (12.9 Ω-cmil/ft for Cu, 21.2 for Al at 75°C)
I Load current in Amperes
L One-way circuit distance in Feet
V_drop Maximum allowable voltage drop in Volts (e.g. 3% of supply voltage)
Frequently Asked Questions
How to calculate wire size?
To calculate wire size (AWG or kcmil), satisfy two primary electrical criteria: (1) Ampacity: Select a wire gauge whose allowable ampacity in NEC Table 310.16 meets or exceeds circuit load after applying ambient temperature correction and conduit bundling deratings. (2) Voltage Drop: For long branch circuits or feeders, calculate minimum circular mils using CM = (2 × K × I × L) / Vdrop for 1-phase/DC, or (√3 × K × I × L) / Vdrop for 3-phase (K = 12.9 for copper, 21.2 for aluminum) to ensure voltage drop is under 3%.
How does DC wire sizing differ from AC wire sizing?
For a dc wire size calculator, 12 volt wire size calculator, or 12v wire size calculator, voltage drop is critical because low-voltage DC circuits (solar, marine, automotive, battery banks) lose a much larger percentage of voltage over short distances. When using a wire size calculator ac vs wire size calculator dc, AC calculations account for power factor and inductive reactance, while DC relies strictly on loop resistance.
How do you choose between ampacity and voltage drop when sizing wire?
A conductor must satisfy both criteria. First, the wire gauge must be large enough to safely carry the current without exceeding thermal ratings (NEC Table 310.16). Second, for long circuit runs, the wire must often be up-sized to limit voltage drop to under 3% for branch circuits.
How does this compare to the Southwire wire size calculator?
Our tool functions as a full southwire wire size calculator alternative with support for both AC single/three-phase and DC systems, multiple conductor materials (Copper, Aluminum), customizable allowable drop percentages (2%, 3%, 5%), and exact NEC circular mil sizing.