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
Disclaimer: Results are estimates based on standard formulas. Not a substitute for professional advice from a licensed contractor, engineer, or architect. Verify all calculations before making purchasing or construction decisions.
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
Expert Insights
Smart analysis for your Electrical project
80% Load Rule Enforcement
NEC requires circuits loaded to no more than 80% of breaker rating for continuous loads. AI enforces this automatically in all calculations.
GFCI/AFCI Requirements
GFCI: kitchens, baths, garages, outdoors. AFCI: bedrooms, living areas (2023 NEC). AI flags required protection for your circuit type.
Voltage Drop Optimization
Over 3% drop causes motor overheating. AI recommends wire gauge upgrades when your run length would cause excessive voltage drop.
Calculation Formula
VD = (2 x L x I x R) / 1000
R = resistance per 1000 ft (NEC Table 9)
% Drop = (VD / V) x 100
Authority References
Our calculations are based on guidelines and standards from these authoritative sources:
- National Fire Protection Association (NFPA) — NFPA 70 — National Electrical Code (NEC). Learn more
- Underwriters Laboratories (UL) — Wire & Cable Safety Standards. Learn more
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.