Voltage Drop Calculator

What this calculator does

The Voltage Drop Calculator provides fast estimates using standard electrical relationships. Enter Source Voltage, Circuit Type, Current (I) to compute results for real-world electrical scenarios. Use it for quick checks, comparisons, and documentation while planning.

Inputs explained

  • Source Voltage: Supply voltage at the source in volts (V).
  • Circuit Type: Select the circuit or phase type.
  • Current (I): Electrical current in amperes (A).
  • One-Way Wire Length: One-way conductor length for the run.
  • Wire Gauge (AWG): Wire size/gauge.
  • Wire Material: Conductor material such as copper or aluminum.

How it works / Method

The calculator applies the listed formulas to the values you enter and then formats the result in standard units.

Formulas used

  • Vd = 2 x I x R x L / 1000
  • Vd = sqrt(3) x I x R x L / 1000

Units: V in volts (V) I in amperes (A)

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Voltage Drop Calculator

Calculate voltage loss in electrical wires

V
A
ft
Result
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Formulas

1-PhaseVd = 2 × I × R × L ÷ 1000
3-PhaseVd = √3 × I × R × L ÷ 1000

NEC Guidelines

Circuit TypeMax Drop
Branch Circuits3%
Feeders2%
Total Combined5%

Wire Resistance (Ω/1000ft)

AWGCopperAluminum
142.5254.04
121.5882.54
100.9991.60
80.6281.00

Related

Wire GaugeOhm's Law

Step-by-step example

Scenario: 100A load, 200ft of #2 AWG copper, single-phase.

Formula: Vdrop = (2 x I x L x R) / 1000

  1. Resistance = 0.159Ω per 1000ft for #2 AWG
  2. Vdrop = (2 x 100 x 200 x 0.159) / 1000
  3. Vdrop = 6.36V (2.65% at 240V)

Result: 6.36V drop (2.65%)

Use cases

  • Estimate conduit fill or voltage drop for planning.
  • Compare wire sizes and run lengths at a high level.
  • Document assumptions for preliminary layouts.
  • Create quick checks before code-compliant design.

Assumptions & limitations

  • Results are estimates and may be rounded; small differences are expected.
  • Inputs assume steady-state values; transient and surge effects are not modeled.
  • Voltage can vary by supply, load, and location; use measured values when possible.
  • Power factor varies by load type; use a realistic value for inductive equipment.
  • Wiring rules and safety codes vary by jurisdiction; consult a licensed electrician for installation decisions.

Sources & references

Related calculators

Frequently Asked Questions

The Voltage Drop Calculator provides a high-level estimate based on your inputs. It is useful for early planning and quick checks. Results depend on conductor type, length, and installation details. Codes vary by jurisdiction and installation method. Use this tool for planning, not final specifications. This calculator is intended for planning and comparison, not for final engineering approval. This calculator is intended for planning and comparison, not for final engineering approval.

Follow the electrical code required in your location. NEC applies in the United States and IEC-based rules apply elsewhere. Codes include limits based on insulation, bundling, and temperature. This calculator cannot capture every rule or exception. Confirm results with the applicable code and a licensed professional. This calculator is intended for planning and comparison, not for final engineering approval.

Accuracy depends on how closely your inputs match the real installation. Conductor material and temperature affect resistance. Number of conductors and bundling affect allowable limits. Use measured lengths where possible. Treat the output as a planning estimate. This calculator is intended for planning and comparison, not for final engineering approval. This calculator is intended for planning and comparison, not for final engineering approval.

The calculator assumes the voltage and power factor you provide. Utility voltage can vary throughout the day. Power factor can be lower for inductive equipment. Use conservative inputs if you are unsure. Verify with measured values for critical work. This calculator is intended for planning and comparison, not for final engineering approval. This calculator is intended for planning and comparison, not for final engineering approval.

No. This tool is for education and early planning only. Final sizing must follow code and local inspection rules. Utility requirements and equipment ratings must be checked. Use a licensed electrician or engineer for installation decisions. Document assumptions for any preliminary estimates. This calculator is intended for planning and comparison, not for final engineering approval. This calculator is intended for planning and comparison, not for final engineering approval.

Length, load current, and conductor size drive most outcomes. Conduit fill also depends on insulation type and conductor count. Small changes can alter the result noticeably. Double-check unit conversions and run length. Use measured values when possible. This calculator is intended for planning and comparison, not for final engineering approval. This calculator is intended for planning and comparison, not for final engineering approval.