Voltage Drop Calculator
Check whether your electrical wire run meets NEC voltage drop recommendations. Enter the wire gauge, one-way distance, load current, and source voltage to calculate the voltage drop, percentage, and voltage at the load end.
Circuit Details
Full Breakdown
Wire Resistance
Total Wire Length
Voltage Drop
Drop Percentage
Voltage at Load
NEC 3% Limit (branch)
NEC 5% Limit (total)
How to Use This Calculator
- Select the source voltage and phase configuration.
- Enter the load current in amps.
- Enter the one-way distance from the panel to the load.
- Select the wire gauge and conductor material.
- Click "Calculate Voltage Drop" to see the drop and NEC compliance.
The Formula
Single Phase: VD = 2 × Length × Resistance × Amps ÷ 1000
Three Phase: VD = √3 × Length × Resistance × Amps ÷ 1000
Drop % = (VD ÷ Source Voltage) × 100
Voltage at Load = Source Voltage − VD
Three Phase: VD = √3 × Length × Resistance × Amps ÷ 1000
Drop % = (VD ÷ Source Voltage) × 100
Voltage at Load = Source Voltage − VD
Resistance values are per NEC Chapter 9 Table 8 at 75°C. NEC recommends max 3% drop for branch circuits and 5% total (feeder + branch). These are recommendations, not code requirements — but exceeding them can cause equipment problems.