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DIY Cost Tools

DIY Cost Tools

Wire Resistance Calculator

Calculate conductor resistance, voltage drop, and heat loss from resistivity, length, cross-sectional area, and current.

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.

Total conductor resistance0.41376 Ω
Voltage drop4.1376 V
Conductor heat loss41.376 W
Resistance per path length0.20688 Ω

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

Resistance = resistivity × length ÷ area. Total resistance multiplies one path by the entered path count; voltage drop = I × R and heat loss = I²R.

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

Material resistivity = 1.724e-8 Ω·m; One-way conductor length = 30 m; Cross-sectional area = 2.5 mm²; Number of current-carrying path lengths = 2; Current = 10 A. The calculator returns Total conductor resistance = 0.41376 Ω; Voltage drop = 4.1376 V; Conductor heat loss = 41.376 W; Resistance per path length = 0.20688 Ω.

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

Limitations and safety

Resistivity changes with temperature and material condition. This page does not select wire size, insulation, ampacity, overcurrent protection or code compliance.

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 the default path count two?

A common two-wire circuit has an outgoing and return conductor, each carrying the same current over the 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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