Voltage Drop

Pulling a long run and not sure the wire is big enough? Voltage Drop turns your circuit type, voltage, load current, run length and conductor into a drop percentage you can act on — updated as you type.

HOW IT WORKS
Pick DC, 1-phase or 3-phase. Enter source voltage, load current and the one-way run length, then choose copper or aluminum and a wire size in AWG or mm². The drop, the voltage left at the load, the power lost in the conductor and the loop resistance all update instantly.

WHAT YOU GET
- Voltage drop in volts and percent, with the voltage actually reaching your load
- Wire loss in watts — the power burned as heat in the conductor
- Smallest wire size that stays within the 3% guideline, one tap to apply it
- DC, single-phase and balanced three-phase, each with the correct formula
- Copper and aluminum, stranded or solid, with conductor temperature you can set
- AWG 14 through 4/0 and IEC sizes from 1.5 mm² to 240 mm²
- Save up to 10 recent calculations and reload any of them
- Works without an internet connection for the calculation itself

ONE-WAY LENGTH, NOT TOTAL WIRE
Enter the distance from the source to the load. The return conductor is already in the formula. This is the single most common mistake in voltage drop math — put in the round-trip length and every answer comes out twice as large.

BUILT FOR
- Electricians sizing a long branch circuit or a sub-panel feeder
- Solar and battery installers working at 12 V, 24 V or 48 V, where a small drop is a large percentage
- RV, marine and automotive wiring, where runs are long and voltage is low
- Apprentices learning how length, current and conductor size pull against each other

HOW THE NUMBERS ARE CALCULATED
Drop is computed as k × L × I × ρ(T) / A, with k = 2 for DC and single-phase and √3 for balanced three-phase. Conductor resistivity is corrected for the temperature you enter. AWG areas follow the ASTM B258 geometric definition, and the resulting copper resistance matches published Ω/1000 ft tables across 14 AWG to 4/0.

NOTES ON SCOPE
This app calculates physical voltage drop and conductor loss. It does not rate ampacity, size breakers or overcurrent protection, and it does not judge code compliance. The 3% and 5% figures are widely used reference guidelines, not a code ruling. Always confirm against your local electrical code and the equipment manufacturer's data before wiring.