Wire Gauge, Voltage Drop and Power Loss Calculator
Conductor resistance, voltage drop and I²R power loss for a given AWG / mm² wire, length, current and temperature — including contact resistance.
Inputs
Results
Drop above 5% of supply is flagged — many designs allow far less.
Smallest wire for an allowed drop
Copper at 20 °C: ρ = 1.724 × 10⁻⁸ Ω·m, temperature coefficient 0.00393 / °C. AWG diameter d = 0.127 mm × 92^((36 − n) / 39). Stranded wire has slightly higher resistance than solid wire of the same AWG — use the datasheet value if you have it.
This tool does not give a current rating. Allowable current depends on insulation, bundling, ambient temperature and the applicable standard — check the wire and connector datasheets.
Frequently asked questions
How do I calculate the voltage drop of a wire?
Voltage drop = current × resistance of the whole loop. Conductor resistance is R = ρ·L / A, and the loop includes both the outgoing and return conductors. Copper resistance rises by roughly 0.39 % per °C, which is why the calculator asks for the wire temperature.
Should I add contact resistance?
Each mated contact pair adds a small resistance, usually given in milliohms in the connector datasheet. At high current this adds measurable voltage drop and heat (I²R), so include one value per connector in the path.
For preliminary assessment only — the final decision must follow the manufacturer’s datasheet and the applicable NEC / IEC / UL standards. Results are calculated from the standard formulas stated on this page and are for design estimates only. They are not a rating of any specific part — always confirm current, voltage, temperature and environment limits against the manufacturer’s datasheet for the part you intend to use.
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Tell us what you are designing — our engineers can suggest series and second-source options.
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