Wire size calculator for AC applications

Use this calculator to determine the indicative copper and aluminum wire sizes (AWG ) wire size for single phase AC  applications. To obtain the wire gauge, you need to provide the following information to the calculator:

  • the supply voltage (V)
  • load current (A)
  • one-way length of cable (feet)

Note: This information is a guide. You should still consult a professional when designing your AC application.


  • Wire length used is the one way length of wire from the voltage source to the appliance
  • Resistance values used in the calculator are based on alternating-current resistance values for 600-Volt Cables, 3-Phase, 60 Hz, 75°C (167°F) — Three Single Conductors in Conduit. 
  • Resistance values assume a fully loaded conductor at that temperature. Resistance  for conductors  hence voltage drop at different  temperatures, stranding may vary. 

Worked example using the calculator – calculating voltage drops

What is the voltage drop for 4 gauge wire, carrying 15 amps over 200 feet at 120 V?

Using the calculator, the voltage drop is 2% with a final voltage of  117.6V.

Formula for calculating AC Voltage drop

The AC voltage drop for single phase can be found from the formula = I*R where:

  • I is the alternating current flowing
  • R is the alternating current resistance for the conductor based on NEC Table 9.

Why you should minimize voltage drops

Voltage drops results in wasted power along the cable run and a reduced voltage for the appliance which may cause the appliance not to work properly.

To ensure that your appliance receives its recommended minimum operating voltage, always select a wire gauge for the cable length such that the final voltage for the appliance meets your appliance voltage requirements (ideally not more than 3%  for branch circuits).

2 Effective ways of minimizing voltage drops

# 1. Avoid unnecessary long cable runs

For example, at 120V,  an appliance drawing 10A over 10 AWG wire with the one way cable length to the appliance at 90 feet results in a  voltage drop of about 2%. 

Should this  distance double (180 feet), then the voltage drop increases to 4% resulting in more power wastage and possibly the appliance may not work properly.

Fix: To maintain the voltage drop (2%) while maintaining the cable length, decrease the wire gauge to 6 AWG.

# 2. For appliances with a high power consumption, use a lower AWG (thicker wire)

Larger appliances (larger loads) require more current which results in a bigger voltage drop for the same distance. Therefore to reduce the drop, you need to increase the size of wire, lower gauge. 

For example, at 120V, you have 3% voltage drop when powering an appliance that draws 10A load over 12 AWG wire at a one way distance for the load of 70ft. 

If a larger appliance (draws more current) is connected drawing 15A as an example,  to maintain the same wire gauge and 2% voltage drop, one way cable should be 61 feet.


  1. If this is not possible to move the load (reduce the cable length, you may use a thicker cable, 10AWG.
  2. Double the voltage to 240V if the load can take it which would allow you to extend the load up to 123 feet!

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