Step-by-Step Voltage Drop Calculator
See the voltage drop math, conductor checks, and final recommendation in one place.
This tool uses the standard resistance method with NEC Table 8 conductor resistance at 75 C. For detailed AC impedance, conduit, and power factor effects, confirm final design decisions in the full AC calculator.
Circuit Inputs
Pick a system and the page will show each sizing step.
Calculation Steps
Formula, substitutions, and conductor checks
Calculate the allowable voltage drop
Allowable drop = source voltage x target drop percentage
Select the correct voltage drop formula
DC and single-phase circuits use a factor of 2. Three-phase circuits use 1.732.
Substitute the project values
The tool then checks conductor resistance values from smallest to largest until one passes.
Step 4: Candidate conductor checks
| Wire | R (ohm/kft) | Drop | Percent | Status |
|---|---|---|---|---|
| 1 | 0.1540 | 0.92 V | 0.77% | Pass |
| 2 | 0.1940 | 1.16 V | 0.97% | Pass |
Engineering Notes
Use one-way circuit length in the input field. The formula factor already accounts for the full conductor path in DC and single-phase work.
This page is intentionally optimized for transparency. It shows the resistance-based sizing path so estimators, electricians, and engineers can explain why a given wire size passes or fails.
For final AC design on long runs, motors, low power factor loads, or magnetic conduit systems, verify the result with the dedicated AC calculator because impedance effects can increase actual drop.