Wire Ampacity Calculator

Wire ampacity is the maximum current a wire can safely carry without overheating. Choosing the right wire gauge prevents fires, voltage drop issues, and equipment damage.

American Wire Gauge (AWG) ampacity ratings (copper, 60°C insulation):

• 18 AWG: 5 amps (lamp cords, low-power devices)
• 16 AWG: 10 amps (extension cords, light fixtures)
• 14 AWG: 15 amps (household circuits — lights, outlets)
• 12 AWG: 20 amps (kitchen outlets, bathroom circuits)
• 10 AWG: 30 amps (dryers, water heaters, A/C)
• 8 AWG: 40 amps (ranges, large A/C units)
• 6 AWG: 55 amps (sub-panels, hot tubs)
• 4 AWG: 70 amps (feeder circuits)
• 2 AWG: 95 amps (large sub-panels)
• 1/0 AWG: 125 amps (main service entrance)

Voltage drop is the loss of voltage over distance. Long wire runs cause more voltage drop, requiring a larger gauge wire.

Voltage Drop = (2 × Length × Current × Resistance per foot) / 1000

Acceptable voltage drop:

• General: 3% maximum
• Motor circuits: 3% for branch circuit, 5% total
• Sensitive electronics: 2% or less

To compensate for voltage drop on long runs, go up one or two wire gauges. For example, a circuit that normally needs 14 AWG at 50 feet might need 12 AWG at 100 feet.

Wire material matters:

• Copper is the standard. Higher conductivity, more expensive.
• Aluminum is used for larger feeders. Must be oversized by about 2 gauge numbers compared to copper.

Temperature rating of the insulation also affects ampacity. Higher-rated insulation (75°C or 90°C) allows more current. The ratings above are for 60°C, which is the most conservative.