Voltage Drop Calculator

Wire / cable voltage drop calculator and how to calculate.

* @ 68°F or 20°C

** Results may change with real wires: different resistivity of material and number of strands in wire.

*** For wire length of 2x10ft, wire length should be 10ft.

Wire gauge calculator

Voltage drop calculations

DC / single phase calculation

The voltage drop V in volts (V) is equal to the wire current I in amps (A) times 2 times one way wire length L in feet (ft) times the wire resistance per 1000 feet R in ohms (Ω/kft) divided by 1000:

V_{drop (V)} = I_{wire (A)} ×R_wire(Ω)

= I_{wire (A)} × (2 × L_(ft)× R_wire(Ω/kft) / 1000_(ft/kft))

The voltage drop V in volts (V) is equal to the wire current I in amps (A) times 2 times one way wire length L in meters (m) times the wire resistance per 1000 meters R in ohms (Ω/km) divided by 1000:

V_{drop (V)} = I_{wire (A)} ×R_wire(Ω)

= I_{wire (A)} × (2 × L_(m)× R_{wire (Ω/km)} / 1000_(m/km))

3 phase calculation

The line to line voltage drop V in volts (V) is equal to square root of 3 times the wire current I in amps (A) times one way wire length L in feet (ft) times the wire resistance per 1000 feet R in ohms (Ω/kft) divided by 1000:

V_{drop (V)} = √3 ×I_{wire (A)} × R_wire(Ω)

= 1.732 × I_{wire (A)}× (L_(ft) × R_wire(Ω/kft) / 1000_(ft/kft))

The line to line voltage drop V in volts (V) is equal to square root of 3 times the wire current I in amps (A) times one way wire length L in meters (m) times the wire resistance per 1000 meters R in ohms (Ω/km) divided by 1000:

V_{drop (V)} = √3 ×I_{wire (A)} × R_wire(Ω)

= 1.732 × I_{wire (A)}× (L_(m) × R_{wire (Ω/km)} / 1000_(m/km))

Wire diameter calculations

The n gauge wire diameter d_n in inches (in) is equal to 0.005in times 92 raised to the power of 36 minus gauge number n, divided by 39:

d_{n (in)} = 0.005 in × 92^(36-n)/39

The n gauge wire diameter d_n in millimeters (mm) is equal to 0.127mm times 92 raised to the power of 36 minus gauge number n, divided by 39:

d_{n (mm)} = 0.127 mm × 92^(36-n)/39

Wire cross sectional area calculations

The n gauge wire's cross sercional area A_n in kilo-circular mils (kcmil) is equal to 1000 times the square wire diameter d in inches (in):

A_{n (kcmil)} = 1000×d_n²= 0.025 in² × 92^(36-n)/19.5

The n gauge wire's cross sercional area A_n in square inches (in²) is equal to pi divided by 4 times the square wire diameter d in inches (in):

A_{n (in}2₎ = (π/4)×d_n²= 0.000019635 in² × 92^(36-n)/19.5

The n gauge wire's cross sercional area A_nin square millimeters (mm²) is equal to pi divided by 4 times the square wire diameter d in millimeters (mm):

A_{n (mm}2₎ = (π/4)×d_n²= 0.012668 mm² × 92^(36-n)/19.5

Wire resistance calculations

The n gauge wire resistance R in ohms per kilofeet (Ω/kft) is equal to 0.3048×1000000000 times the wire's resistivity ρ in ohm-meters (Ω·m) divided by 25.4² times the cross sectional area A_n in square inches (in²):

R_{n (Ω/kft)} = 0.3048 × 10⁹ ×ρ_(Ω·m) / (25.4²× A_{n (in}2₎)

The n gauge wire resistance R in ohms per kilometer (Ω/km) is equal to 1000000000 times the wire's resistivity ρ in ohm-meters (Ω·m) divided by the cross sectional areaA_n in square millimeters (mm²):

R_{n (Ω/km)} = 10⁹× ρ_(Ω·m) / A_{n (mm}2₎

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