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DIY Cost Tools

DIY Cost Tools

Two-Wire Voltage Drop Calculator

Estimate DC or single-phase two-wire voltage drop from current, one-way length, and conductor resistance.

Use the units shown beside each field. Decimal and scientific notation are accepted for non-integer fields; blanks, commas, fractions and non-finite entries are rejected.

Round-trip conductor resistance0.3176 Ω
Voltage drop6.352 V
Voltage drop5.293333333%
Estimated load voltage113.648 V
Conductor power loss127.04 W

The displayed results apply to the default example. Enable JavaScript to calculate other inputs.

How to use this calculator

  1. Replace the example values with measurements or ratings for the exact vehicle, circuit, component or system.
  2. Keep every value in the labeled unit and use manufacturer data where available.
  3. Select Calculate, then review the result together with the limitations and safety notes.

Formula and method

Round-trip resistance = 2 × one-way feet × Ω per 1,000 ft ÷ 1,000. Voltage drop = current × resistance.

Calculations run in your browser. Results are hidden whenever an input changes or validation fails, preventing an older result from being mistaken for a new calculation.

Worked example

Load current = 20 A; One-way conductor length = 100 ft; Conductor resistance = 1.588 Ω/1000 ft; Source voltage = 120 V. The calculator returns Round-trip conductor resistance = 0.3176 Ω; Voltage drop = 6.352 V; Voltage drop = 5.293333333%; Estimated load voltage = 113.648 V; Conductor power loss = 127.04 W.

The worked example uses the same defaults shown in the interface, allowing the formula and displayed result to be checked together.

Limitations and safety

This does not select conductor size or verify ampacity. Resistance changes with temperature, and AC reactance, phase configuration, terminals and code limits may matter.

This is an educational planning model. Confirm ratings, tolerances, code requirements and safe procedures with manufacturers and qualified professionals before purchasing, modifying, wiring or operating equipment.

Frequently asked questions

Why is one-way length doubled?

A two-wire circuit has an outgoing and return conductor, so the current travels twice the entered one-way distance.

Why does the calculator reject my entry?

Each field shows its supported range. Whole-number fields reject decimals, and all fields reject blanks, words, comma-formatted numbers, fractions and non-finite values.

How should I use the displayed precision?

Keep extra digits while checking the calculation, then round to the precision supported by the measurements, component tolerances and published ratings.

Review notes and reference

Reviewed October 4, 2026. The formula and default example were checked together. The script was tested for defaults, input boundaries, invalid formats, condition-specific errors and recovery after an error. Reference: OSHA electrical safe-work requirements. Explanations and examples are original.

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