Voltage Drop Calculator
Calculate voltage drop for your wiring run
Select wire size
Expected or breaker current
120V or 240V
Distance to load
Single or three phase
Voltage Drop
—
V
Drop Percentage
—
%
Voltage at Load
—
V
How to Use This Calculator
Our calculator helps determine if your wire size is adequate for the run length.
- Select wire gauge
- Enter current and voltage
- Enter wire length
- If drop > 3%, increase wire gauge
AI Insights
Smart analysis for your project
Smart Estimates
Our AI cross-references material costs, regional pricing, and project complexity for more accurate estimates.
Waste Optimization
AI-calculated waste factors based on project type, not flat percentages. Saves 5-15% on material costs.
Best Practices
Recommendations derived from building codes, contractor data, and thousands of completed projects.
Calculation Formula
VD = (2 x L x I x R) / 1000
R = resistance per 1000 ft (NEC Table 9)
% Drop = (VD / V) x 100
Frequently Asked Questions
What is acceptable voltage drop?
NEC recommends max 3% for branch circuits and 5% total (feeder + branch).
How do I reduce voltage drop?
Increase wire gauge, decrease circuit length, or increase voltage.