Wire Size Calculator

The Wire Size Calculator determines the correct electrical wire gauge (AWG) for safe installations based on amperage, distance, voltage, and wire material. Proper wire sizing is critical for electrical safety—undersized wire can overheat, melt insulation, and cause fires.

The National Electrical Code (NEC) requires that voltage drop not exceed 3% for branch circuits and 5% for the total system (feeder + branch). Our calculator uses the 3% threshold, which is the more conservative and commonly applied standard for residential and commercial installations.

American Wire Gauge (AWG) is the standard wire sizing system in North America. Lower gauge numbers indicate thicker wire with higher current capacity. Common residential sizes include: 14 AWG for 15A circuits (lighting), 12 AWG for 20A circuits (outlets), 10 AWG for 30A circuits (dryers), 8 AWG for 40A circuits (ranges), and 6 AWG for 50A circuits (large appliances).

For long wire runs, you often need to upsize wire beyond the minimum ampacity requirement to keep voltage drop within acceptable limits. This is especially important for detached garages, outbuildings, well pumps, and other loads far from the electrical panel.

Copper wire is the standard for most residential branch circuits due to its excellent conductivity (resistivity of 10.37 Ω·cmil/ft). Aluminum wire is about 61% as conductive (resistivity 17.02) but costs significantly less per foot. Aluminum is commonly used for service entrance conductors, feeder wires, and large circuits where cost savings are substantial. When using aluminum, always use anti-oxidant compound and connectors rated for aluminum.

Always consult a licensed electrician and local building codes before performing electrical work. Wire sizing is just one aspect of safe electrical design—proper breaker sizing, grounding, conduit fill, ambient temperature derating, and installation methods all affect the final design.