Wire and Cable Calculator

Electrical Engineering & NEC 2023 Wire Sizing Metrology

Conductor sizing balances thermodynamic ampacity heating and Ohm's Law voltage drop:

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• NEC Voltage Drop Formula (Single-Phase Circuits)**:

Δ V = (2 × K × I × L) / (CMIL)

\% Voltage Drop = ((Δ V) / (V_nominal)) × 100

• Resistivity Constants (K): Copper K = 12.9\ Ω·cmil/ft | Aluminum K = 21.2\ Ω·cmil/ft

• NEC Section 210.19 Limit: Maximum 3\% drop on branch circuits.

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• NEC Table 310.16 Standard Conductor Capacities & Circular Mils**:

• 14 AWG (4,110 CMIL): 15 Amps (Copper)

• 12 AWG (6,530 CMIL): 20 Amps (Copper) / 15 Amps (Aluminum)

• 10 AWG (10,380 CMIL): 30 Amps (Copper) / 25 Amps (Aluminum)

• 8 AWG (16,510 CMIL): 50 Amps (Copper) / 40 Amps (Aluminum)

• 6 AWG (26,240 CMIL): 65 Amps (Copper) / 50 Amps (Aluminum)

• 4 AWG (41,740 CMIL): 85 Amps (Copper) / 65 Amps (Aluminum)

• 2 AWG (66,360 CMIL): 115 Amps (Copper) / 90 Amps (Aluminum)

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• Standard Circuit Sizing Benchmarks**:

• 15A Shed Run (120V, 100 ft, Cu): 10 AWG | 1.99% Drop | 15A Breaker

• 20A Circuit (120V, 75 ft, Cu): 8 AWG | 1.95% Drop | 20A Breaker

• 50A EV Charger (240V, 60 ft, Cu): 6 AWG | 1.31% Drop | 50A Breaker

• 60A Subpanel (240V, 150 ft, Al): 2 AWG Al | 2.29% Drop | 60A Breaker

How to Use This Calculator

Enter your Circuit Voltage & Phase — choose from 120V Single-Phase (Standard Lighting & Outlets), 240V Split-Phase (EV Charger, Dryer, Water Heater, Subpanel), 208V 3-Phase (Commercial Lighting & Motors), Circuit Load Current (Amperes) (e.g. 20 in amps), One-Way Distance from Panel (e.g. 75 in ft), Conductor Material — choose from Copper (Cu - High Conductivity / Standard Residential), Aluminum (Al - Lightweight / Large Subpanel Feeder), Maximum Allowable Voltage Drop (NEC) — choose from 2% (High-Precision Sensitive Electronics / Solar), 3% (NEC Recommended Branch Circuit Limit), 5% (NEC Maximum Total Combined Feeder + Branch), and Electrical Circuit Benchmark — choose from Custom Electrical Circuit, 20A Circuit (120V, 75 ft, Copper) → 8 AWG (1.95% Drop / Upsized for <3% Drop), 50A Level 2 EV Charger (240V, 60 ft, Copper) → 6 AWG (1.31% Drop). Measure twice before entering dimensions — small measurement errors scale up significantly in material estimates.

The Formula

Conversion factors (to SI base unit or reference unit):

dr: 3.0

cmil: 4110

cuAmp: 15

alAmp: 15

Worked Example

An electrician wiring a full 20A load at 75 feet from the breaker panel determines that 12 AWG would drop nearly 5% voltage (5.9V), upsizing to 8 AWG copper to guarantee a safe 1.95% drop and prevent equipment damage.

Understanding Your Result

Construction estimates are starting points — site conditions, material specifications, and local code requirements will affect final quantities and costs. Always obtain at least three contractor bids for major projects. Local building departments can confirm permit requirements and inspection milestones. Add waste factors appropriate to the material type and complexity: 10% for simple rectangular shapes, 15–20% for complex geometries or custom cuts.