Voltage Drop Calculator

The root-mean-square (RMS) voltage at the source of the circuit. Measured line-to-line for three-phase or line-to-neutral for single-phase circuits. Input range is from 1 to 1,000 V.
Balanced line ampacity at the load. This value is the current at maximum load. Input range is from 1 to 1,000 A.
Identical sets of parallel conductors between the source and load. All parallel conductors are assumed to be the same size.
Power factor at the load. Input range is from 0 to 1.0. 0 is purely reactive (an ideal capacitor or inductor) and 1.0 is purely resistive. Typical values for real loads are from 0.8 to 1.0.
AWG, _/0, or kcmil
Trade size of the current-carrying conductors (assumes the current is balanced). Used to look up the resistance and reactance for that specific conductor per NEC Table 9. Note: #12 aluminum resistance values assumed for #14 aluminum.
Copper or Aluminum current-carrying conductors.
One-way conductor length from source to the load. Input range is from 1 to 10,000.
Conduit material impacts conductor reactance. Choices are Steel, PVC, and Aluminum.
The ambient temperature in °C. NEC Table 9 resistances are adjusted if the ambient temperature is not 75°C.
Load demand factor, an optional field. This value is used to scale the load current when calculating energy losses from the cable. Conductors are typically sized for the maximum load though average load may be less.


This calculator uses the IEEE Red Book (Standard 141) phasor method. This is more accurate than other methods that ignore power factor or only consider conductor size. Tabulated voltage drop factors can be found here for quick reference. Calculating the expected voltage drop when sizing conductors is critical to ensure electrical loads have adequate voltage.

Conductors sized large may drive up initial capital costs but have lower energy losses where the demand factor is high. Conversely conductors sized small will have lower capital costs but may have excessive voltage drop for the load and higher energy losses. It’s also good engineering practice to size the conductor accounting for future expansion.

Additional factors to consider are conductor terminations, insulation ratings and the cable bend radius.

Questions or comments? I appreciate feedback: brendon.bruns@gmail.com