How to use the Voltage Drop Calculator
Estimate voltage drop from load current, circuit resistance, resistance unit with the Voltage Drop Calculator. It includes Known circuit resistance, Conductor and wire gauge, Direct resistance and reactance, Direct impedance workflows, so choose the one that matches the values you actually know. Use it to check a practical estimate, paying close attention to the selected units and assumptions.
Step by step
- For the Voltage Drop example, select Known circuit resistance and enter load current, circuit resistance, resistance unit, source voltage. Keep each value in the unit displayed beside its field.
- Review the selected Voltage Drop workflow and inputs, then read voltage drop in the result panel.
- Change one Voltage Drop assumption at a time to compare scenarios. Use Reset to restore this tool's worked example values.
How the calculation works
Known resistance uses Vdrop = I×R. Conductor mode uses standard circular-mil AWG area and K=12.9 copper or 21.2 aluminum Ω·cmil/ft; single-phase uses 2KIL/CM and three-phase uses √3KIL/CM. Advanced workflows include conduit/cable installation, parallel conductors, power factor, direct R/X or impedance, metric and long-distance runs, and resistance units.
Worked example
To reproduce the Voltage Drop worked example, reset the calculator. Select the Known circuit resistance workflow. Use load current 10 A; circuit resistance 0.2 Ω; resistance unit Ω; source voltage 120 V. The result is voltage drop of 2 V. I × total circuit resistance. Review the displayed units before comparing the result.
Understanding the result
The Voltage Drop reports voltage drop. Use it to check a practical estimate, paying close attention to the selected units and assumptions. Check the entered units and assumptions before using the result for purchasing, construction, engineering, or safety decisions.
How to check the answer
Check the Voltage Drop result by reversing the conversion or recomputing voltage drop from load current, circuit resistance, resistance unit. For construction, electrical, weather, or purchasing decisions, compare the result with the applicable specification or professional guidance.
Common questions
What does the Voltage Drop calculate?
Estimate voltage drop from load current, circuit resistance, resistance unit with the Voltage Drop Calculator.
Which inputs does the Voltage Drop example use?
The worked example uses load current, circuit resistance, resistance unit, source voltage in the Known circuit resistance workflow. Other workflows can show different fields. Keep the chosen workflow and units with the result when comparing calculations.
Is the Voltage Drop result exact?
Check the entered units and assumptions before using the result for purchasing, construction, engineering, or safety decisions. Recheck load current, circuit resistance, resistance unit and use voltage drop only for a decision where that level of precision is appropriate.