Voltage Drop Calculator

Voltage Drop Calculator

Calculate voltage drop for DC, AC single-phase, and AC 3-phase circuits with AWG/metric wire sizes, NEC compliance check, and wire size recommendations

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Voltage Drop Calculator

Calculate voltage drop using wire material, gauge, circuit length, and load current. Supports DC, single-phase, and 3-phase AC systems.

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Wire Size Finder

Find the minimum wire gauge needed to keep voltage drop within a specified percentage. Enter your circuit parameters and target max drop.

NEC recommends max 3% feeder, 5% total
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AWG Wire Reference Table

Complete AWG reference with diameter, area, and resistance data for copper and aluminum at 20°C (68°F).

AWG Dia (in) Dia (mm) Area (kcmil) Area (mm²) Cu Ω/km Cu Ω/kft Al Ω/km Al Ω/kft
About AWG (American Wire Gauge)
AWG is a standardized system used in North America for wire diameters. Lower AWG number = larger wire = lower resistance. Every 6-gauge decrease doubles the wire diameter; every 3-gauge decrease doubles the cross-sectional area. Values shown at 20°C (68°F).
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Understanding Voltage Drop

Learn about voltage drop causes, formulas, and NEC recommendations.

What is Voltage Drop?
Voltage drop is the reduction in voltage as electrical current flows through a conductor. It is caused by the resistance (DC) or impedance (AC) of the wire. The longer the wire and the smaller the gauge, the greater the voltage drop.
Calculation Formulas
DC / Single-Phase AC:
V₂ᶴᶳᶱ = 2 × I × R × L

3-Phase AC:
V₂ᶴᶳᶱ = √3 × I × R × L

Where: I = Current (A), R = Resistance per unit length (Ω/m or Ω/ft), L = One-way length

Wire Resistance:
R = ρ × L / A   (ρ = resistivity, A = cross-sectional area)
NEC Recommendations
Maximum 3% voltage drop for branch circuits or feeders
Maximum 5% total voltage drop (feeder + branch circuit combined)

Excessive voltage drop causes: lights to flicker or burn dimly, heaters to perform poorly, motors to run hotter and burn out, electronics to malfunction.
Wire Material Resistivity
Silver: 1.59 × 10⁻⁸ Ω·m (best conductor)
Copper: 1.72 × 10⁻⁸ Ω·m (most common)
Gold: 2.44 × 10⁻⁸ Ω·m
Aluminum: 2.65 × 10⁻⁸ Ω·m (lighter, cheaper)
Nickel: 6.99 × 10⁻⁸ Ω·m
Carbon Steel: 1.43 × 10⁻⁷ Ω·m
Nichrome: 1.10 × 10⁻⁶ Ω·m (resistance wire)
4 Key Factors Affecting Voltage Drop
1. Wire Material — Copper conducts ~55% better than aluminum. Silver is slightly better than copper.
2. Wire Size (Gauge) — Larger diameter = lower resistance. AWG 10 has ~3.3x less resistance than AWG 16.
3. Wire Length — Resistance increases linearly with length. Doubling length doubles the drop.
4. Current Load — More current = more drop. Always size wire for the actual load amperage.