Cable Size Calculator — Wire Gauge for Load & Distance
Min Cross-Section Area
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Suggested AWG
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Actual Voltage Drop
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Selecting the Right Wire Gauge for Your Circuit
Choosing the correct cable size is critical for electrical safety, efficiency, and code compliance. This calculator determines the appropriate wire gauge based on the current load, cable run length, voltage, and acceptable voltage drop. Undersized wiring causes excessive heat buildup that degrades insulation and creates fire hazards, while oversized wiring wastes money on unnecessary copper.
The calculation follows NEC (National Electrical Code) guidelines and basic electrical engineering principles. Voltage drop is calculated using V_drop = (2 * Length * Current * Resistivity) / Cross-sectional Area, where the factor of 2 accounts for the round-trip distance of current flow. The NEC recommends keeping voltage drop below 3% for branch circuits and 5% for combined feeder and branch circuits. The calculator selects the smallest standard AWG (American Wire Gauge) size that keeps the voltage drop within acceptable limits while also meeting the ampacity requirements for the given current load.
Proper wire sizing is essential for residential wiring, solar panel installations, EV charger circuits, workshop equipment, and low-voltage landscape lighting. Longer cable runs require larger gauges because resistance increases with length, causing greater voltage drop. For DC circuits like solar and battery systems, voltage drop is especially important because operating voltages are lower, making the same absolute drop a larger percentage of the total voltage. Always verify your calculations with a licensed electrician for permanent installations.
Frequently Asked Questions
Why does voltage drop matter?
Excessive voltage drop causes motors to run hot, lights to dim, and equipment to malfunction. National Electrical Code recommends no more than 3% drop for branch circuits and 5% total from panel to outlet.
Copper vs aluminum wire?
Copper has lower resistivity (better conductivity per size) but costs more. Aluminum requires larger gauge wire for the same ampacity. Aluminum is common for large feeders and service entrance cables.
What about AC vs DC circuits?
This calculator works for both DC and single-phase AC circuits. Three-phase AC circuits use a different formula (multiply by 1.732 instead of 2 for the round-trip factor).