Voltage Drop Calculator
Calculate voltage drop over a wire run from AWG gauge, length, current, and circuit type, with a 3% warning.
Processed locally in your browser — nothing is uploaded.
Voltage Drop Calculator
Distance from source to load, not the round trip.
Results
- Voltage drop
- 1.588 V
- Drop percentage
- 1.32%
- Voltage at the load
- 118.41 V
Based on 20°C copper resistance (aluminum ≈ 1.64× copper) and resistive load. Conductor temperature and power factor shift real-world results — treat this as guidance, not an electrical-code calculation.
About Voltage Drop Calculator
Pick a wire gauge and material, enter the one-way run length, load current, and source voltage, and see the voltage drop, percentage drop, and what actually arrives at the load. DC and single-phase AC use the round-trip (×2) conductor length; three-phase uses the √3 factor.
Resistance values are the standard 20°C annealed-copper table (aluminum ≈ 1.64× copper). Drops above 3% are flagged, matching the common design recommendation for branch circuits.
Common uses
- Check whether a long extension run will brown out a power tool
- Size 12 V wiring in a van, boat, or solar build where drop hurts most
- Verify a feeder run stays inside the 3% guideline
Example
Input
12 AWG copper · 50 ft one-way · 10 A · 120 V single-phase
Output
1.59 V drop (1.32%) · 118.4 V at the load
Limitations
- Conductor temperature, power factor, and conduit effects are not modeled — this is guidance, not an electrical-code calculation.
Frequently asked questions
How much voltage drop is acceptable?
A common design recommendation is to keep branch-circuit drop at or below 3%, which is where this calculator raises a warning. Some designs allow up to 5% combined across feeder and branch circuits.
Why is the wire length doubled in a voltage drop calculation?
Current flows out to the load and back, so a DC or single-phase circuit sees resistance over twice the one-way distance. Enter the one-way length and the calculator applies the ×2 factor itself, or ×√3 for balanced three-phase.
Do my circuit details leave my browser?
No. Wire gauge, lengths, and load figures are processed locally in your browser — nothing about your electrical project is uploaded or stored.
Does voltage drop matter more at 12 V than at 120 V?
Yes. The same 1.5 V drop is 1.25% of a 120 V circuit but 12.5% of a 12 V one, which is why van, boat, and solar wiring needs much thicker conductors for the same power.
How does aluminum wire compare to copper for voltage drop?
Aluminum has about 1.64 times the resistance of copper, so the same gauge drops roughly 64% more voltage. Aluminum runs typically step up one or two gauge sizes to match copper's performance.