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Voltage Drop Calculator

Estimate round-trip voltage drop and remaining voltage from current, length, resistance, and supply.

Voltage Drop Calculator Inputs

Results computed instantly — your data never leaves your device.

Voltage Drop Calculator Results

Real-Time

Voltage drop

17.50 V

Remaining voltage

102.50 V

Drop percentage

14.58%

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How to Use the Voltage Drop Calculator

  1. 1

    Enter load current in amps.

  2. 2

    Enter one-way cable length in feet.

  3. 3

    Enter conductor resistance in ohms per 1,000 feet.

  4. 4

    Enter supply voltage and review drop and remaining voltage.

Formula & Mathematical Basis

Voltage drop = current × (2 × one-way length ÷ 1000) × resistance per 1000 ft.

Variable Key

I

Load current in amps

L

One-way conductor length in feet

R

Conductor resistance in ohms per 1000 feet

📝 The factor of two models a round-trip pair; real installations also depend on conductor temperature, connections, and code requirements.

Step-by-Step Examples

1

Two-wire run

Scenario: A 10 A load, 100 ft one-way, 1.0 Ω/1000 ft, and 120 V supply.

  1. 1.Double the one-way length to 200 ft.
  2. 2.Convert to 0.2 of a 1000-ft resistance unit.
  3. 3.Multiply 10 × 0.2 × 1.0.
  4. 4.Compare the 2 V drop with the 120 V supply.
✅ Drop is 2 V, or about 1.67%, leaving 118 V in the simplified model.

Practical Use Cases

  • Screen a cable run during early design.
  • Compare conductor resistance assumptions.

Common Pitfalls

  • Using total loop length and doubling it again.
  • Confusing resistance per foot with resistance per 1000 feet.
  • Treating this estimate as a code compliance decision.

Frequently Asked Questions

Does this select wire size?

No; it only estimates voltage drop from the entered resistance.

Is the result code compliant?

No; consult applicable electrical codes and a qualified electrician.

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