Voltage Drop Calculator
Calculate voltage drop in wire based on distance and load
A voltage drop calculator estimates the voltage a wire loses from the source voltage, phase, load current, one-way distance, conductor, and wire size on this page.
Calculator Inputs
Circular Mils
Results
Enter values above to see your results
How It Works
Formula: VD = (2 × K × I × L) / CM. (For 3-phase, substitute 2 with √3).
Worked example
Copper 8 AWG at 50 ft
Source voltage:
120V AC (single phase)= 120 VPhase:
Single Phase / DC= Constant 2Load current:
10 A= GivenOne-way distance:
50 ft= GivenConductor:
Copper (K = 12.9)= GivenWire size:
8 AWG (6,530 circular mils)= GivenVoltage drop:
(2 × 12.9 × 10 × 50) / 6530= 1.98 VPercentage drop:
1.98 / 120= 1.65%Voltage at the load:
120 − 1.98= 118.02 VTips & Best Practices
- •NEC recommends a maximum voltage drop of 3% for branch circuits and 5% for feeders.
- •Upsizing wire reduces voltage drop and wasted energy.
Frequently Asked Questions
What is K factor?
It represents the resistivity of the material. Copper is ~12.9, Aluminum is ~21.2.
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