Voltage Drop Calculator (NEC-Compliant, AWG)

Calculate voltage drop for 120V, 240V, 277V, and 480V circuits using AWG wire size, conductor material, current, and circuit length. This voltage drop calculator helps electricians, contractors, and homeowners estimate wire loss, compare copper vs aluminum conductors, and check whether a circuit stays within commonly recommended voltage drop guidelines.

Circuit Details

Results

Voltage Drop (Volts) 0.00 V
Voltage Drop (%) 0.00%

Formula based on conductor resistance values per NEC/NFPA 70. Always verify against the current code edition and local amendments.

Also try:

AWG wire size calculator for ampacity & voltage drop NEC conduit fill calculator — 40% rule AWG wire gauge chart with NEC ampacity values voltage drop reference table — color-coded NEC compliance feeder wire size calculator — 100A/200A service entrance

How to Use This Voltage Drop Calculator

Enter the system voltage, load current, one-way circuit length, wire material, and AWG wire size to estimate voltage drop for your circuit. This calculator supports common US electrical systems, including 120V, 240V, 277V, and 480V installations.

Use it to compare copper and aluminum conductors, evaluate long wire runs, and see when increasing wire size may be necessary. For related conductor sizing questions, see our wire size calculator or compare conductor options in the AWG wire gauge chart.

Why Voltage Drop Matters

Excessive voltage drop can reduce equipment performance, increase heat, and cause motors, lighting, and other electrical loads to operate less efficiently. Longer wire runs, higher current, and smaller conductors all increase voltage drop.

Checking voltage drop is especially useful for subpanels, detached garages, workshops, HVAC equipment, and EV chargers. If your result is too high, the most common fix is increasing conductor size or using a lower-resistance conductor material.

How This Voltage Drop Calculator Works

This calculator estimates voltage drop using conductor resistance values along with system voltage, current, circuit length, wire gauge, and conductor material. Longer runs, higher amp loads, and smaller conductors produce a larger voltage drop percentage.

Enter the one-way circuit length shown in the form, then review both the voltage drop in volts and the percentage drop. If the percentage is above your design target, try a larger AWG size or compare copper vs aluminum results for the same run.

Common Voltage Drop Scenarios

  • 120V branch circuits in homes, garages, and workshops
  • 240V appliance, well pump, and HVAC circuits
  • 277V and 480V commercial lighting and equipment circuits
  • Long feeder runs to sheds, detached buildings, and subpanels
  • Comparing copper vs aluminum wire for the same load and length
  • Choosing a larger AWG conductor to stay within recommended voltage drop limits

Frequently Asked Questions

A common design target is 3% maximum voltage drop for a branch circuit and 5% total for feeder plus branch circuit. This calculator shows both volts and percentage drop so you can quickly see whether your selected conductor is close to that range.

Copper has lower resistance than aluminum, so the same AWG copper conductor usually produces less voltage drop under the same load and length. Aluminum can still be a good choice in some installations, but you may need a larger conductor size to reach the same result.

Use the calculator above and select 240V under System Voltage. The result updates based on voltage, current, wire size, conductor material, and circuit length.

For this calculator, enter the one-way length of the circuit run. The voltage drop calculation accounts for the conductor path as part of the formula used for the selected system.

If your voltage drop percentage is higher than your target, increasing conductor size is the most common solution. This is especially helpful on longer runs and higher-current circuits.

Excessive voltage drop can reduce equipment performance, cause dimming or poor motor operation, and increase heat on longer or more heavily loaded circuits. Keeping drop under control helps electrical systems run more efficiently.