Circuit Analysis calculator
Voltage Drop Calculator
Enter voltage, current, one-way distance, phase, conductor material, and wire size to calculate conductor voltage loss, percent drop, load voltage, and power loss. Use the result to compare the selected conductor against your project voltage-drop target, then review ampacity, termination temperature, routing, and equipment requirements before finalizing the circuit.
Updated July 10, 2026
Enter voltage, current, one-way distance, phase, conductor material, and wire size to calculate voltage loss, percent drop, load voltage, and power loss for your circuit.
Vd = 2 × L × I × R ÷ 1000 (single-phase) | √3 factor for 3-phase
Use the calculator to compare conductor sizes against your voltage-drop target
Example Calculations
More examples. Open to review 4 additional calculation examples.
How to Use
Specify system type (single-phase or three-phase), nominal voltage, load current, one-way conductor length, conductor material, conductor size, and optional operating temperature. The calculator uses standard voltage-drop formulas with conductor resistance values at the selected operating conditions to compute voltage drop, percent drop, load voltage, power loss, and a design-target comparison. Use these results to evaluate conductor sizes and run lengths against project requirements and applicable standards; always confirm final selections against the current electrical code, manufacturer data, and project specifications.
For a complete derivation of the voltage-drop formula Vd = 2 × I × R × L / 1000 plus common NEC design targets, see the Voltage Drop Formulas Guide. If voltage drop is above the project target, use the Wire Size Calculator to compare conductor size, ampacity, and voltage drop together. For conductor ampacity with temperature and bundling corrections, see the Ampacity Calculator. For DC circuits, use the dedicated DC Voltage Drop Calculator.
NEC Voltage Drop Recommendations (210.19(A) Informational Note)
| Circuit Type | Common Design Target | Reasoning / Impact |
|---|---|---|
| Branch Circuits | About 3% | Supports usable equipment voltage for electronics, motors, and lighting. It is a design comparison point, not a standalone NEC pass/fail rule. |
| Feeder + Branch (Total) | About 5% | Total planned drop from the service equipment through feeder and branch conductors. Example: 2% feeder drop plus 3% branch drop. |
Use the calculator first, then compare the result
Use the calculator first for the actual voltage, current, one-way distance, phase, material, and wire size on your circuit. The preset examples are there to prefill common branch-circuit, feeder, and EV-charger scenarios, but the page does not replace the project-specific calculation or the follow-up ampacity and equipment review.
Common Applications
More applications. Open to review 3 additional use cases.
Frequently Asked Questions
What's the difference between NEC recommended voltage drop limits and mandatory requirements?
NEC informational notes commonly reference design targets of about 3% voltage drop for branch circuits and about 5% for feeders plus branch circuits together. These values are recommendations, not enforceable requirements, but following them generally supports good equipment performance and reasonable efficiency. Final limits should be selected based on the applicable code edition, equipment data, and project requirements.
How do I calculate voltage drop for three-phase systems with unbalanced loads?
For unbalanced three-phase loads, calculate voltage drop for each phase separately using single-phase formulas. The phase with the highest current will have the greatest voltage drop. Consider neutral current for wye-connected systems with unbalanced loads.
Should I use AC or DC resistance values for voltage drop calculations?
Many design references use DC resistance values for smaller conductors and AC resistance values for larger sizes to account for skin effect and proximity effect. Check the resistance data source you are using and match the assumptions in your voltage-drop calculation to the applicable standard or manufacturer tables.
How does power factor affect voltage drop calculations?
Power factor affects the relationship between voltage drop and power delivery. For the same power output, lower power factor requires higher current, increasing voltage drop. Use impedance (Z) rather than resistance (R) for accurate calculations with reactive loads.
What voltage drop target should I use for motor circuits?
Many designers start with the same common 3% branch-circuit design target for normal running voltage, then verify motor starting behavior against the actual equipment and project requirements. Starting analysis is outside this calculator because it depends on motor inrush, source impedance, and starter type.
How do I account for temperature effects on conductor resistance?
Conductor resistance increases with temperature. Use the formula R₂ = R₁ × [1 + α(T₂ - T₁)] where α = 0.00393 for copper and 0.00403 for aluminum. Our calculator includes temperature correction factors for accurate results.
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