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Science & Engineering Calculator
Voltage Drop Calculator
Estimate voltage drop, voltage drop percentage and end voltage for copper or aluminum conductors using current, distance, voltage, phase and wire size.
Voltage drop by wire size
Resistance values are approximate ohms per 1,000 ft for copper.
Voltage drop–
Drop percentage–
End voltage–
Status–
Enter circuit details to estimate voltage drop.
Voltage drop formulas
Single phase or DC drop = 2 x current x one-way distance x resistance per foot
Three phase drop = 1.732 x current x one-way distance x resistance per foot
Drop percentage = voltage drop / source voltage x 100
This calculator uses approximate conductor resistance values. Temperature, conduit fill, local code and conductor type can change real installations.
Voltage drop guidance
- About 3% or less is commonly considered a good design target for many branch circuits.
- About 5% or less may be acceptable in some combined feeder and branch situations.
- Long runs, high current and smaller conductors increase voltage drop.
- Electrical work should follow local electrical code and qualified professional guidance.
Voltage Drop Calculator FAQ
What is voltage drop?
Voltage drop is the voltage lost along a conductor because wire has resistance.
How do I reduce voltage drop?
Use a larger wire size, reduce current, shorten the run or increase system voltage where appropriate.
Is 3 percent voltage drop good?
Three percent or less is a common design target for many branch circuits, but local requirements may differ.
Does aluminum wire drop more voltage?
For the same size and length, aluminum has higher resistance than copper, so voltage drop is higher.
Is this a code calculator?
No. It is an estimator. Always verify real electrical installations against local code and professional guidance.
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