Voltage drop calculator
Formula used
The calculator first converts every input into volts, amperes, meters, square meters, ohms, and watts. It then corrects conductor resistivity for the selected operating temperature.
When total loop length is selected, the length already includes outgoing and return paths, so the calculator uses a path factor of one. For a one-way length, it uses two for DC and single-phase circuits or the square root of three for a balanced three-phase circuit.
How to use this calculator
- Choose a preset or keep the custom project option.
- Select DC, single-phase AC, or balanced three-phase AC.
- Enter source voltage and provide current, real power, apparent power, or horsepower.
- Enter the one-way cable length unless your value already represents the complete circuit path.
- Select conductor material, wire size, temperature, and parallel conductor count.
- Set the allowable drop percentage or enter a direct voltage limit.
- Use advanced AC mode when resistance, reactance, and power factor data are available.
- Review voltage at the load, power loss, wire comparison, recommendation, warnings, and charts.
Understanding circuit voltage drop
Why conductors lose voltage
Every practical conductor has electrical resistance. When current flows, that resistance produces a voltage difference between the source and the load. Longer conductors, smaller cross-sectional areas, hotter conductors, and higher current all increase the loss. Copper usually has lower resistance than an equal-sized aluminum conductor, although aluminum can remain economical where larger sizes are practical.
Voltage drop matters because equipment receives less voltage than the source provides. Lamps may dim, heaters may produce less heat, electronics may reset, and motors may draw additional current or develop reduced torque. Low-voltage battery, automotive, marine, solar, and LED circuits are especially sensitive because a small absolute loss can represent a large percentage of the available voltage.
AC resistance and reactance
For direct current, a resistance-only model is often sufficient. Alternating-current feeders may also require reactance. The effect depends on conductor arrangement, spacing, magnetic raceways, frequency, and load power factor. The advanced AC option combines the resistive and reactive components projected along the load-current angle. For detailed installations, use manufacturer impedance data or an engineering cable database.
Choosing an acceptable limit
An acceptable design limit depends on equipment sensitivity, starting performance, local rules, and the relationship between feeders and branch circuits. The percentage control is therefore adjustable. The calculator also accepts a direct voltage limit, which is useful for low-voltage electronics or manufacturer-specific requirements.
A conductor that passes a voltage-drop test does not automatically satisfy ampacity, short-circuit withstand, terminal temperature, insulation, grouping, ambient correction, protection, grounding, or mechanical requirements. The comparison table includes an approximate ampacity screen only to prevent an obviously undersized recommendation. Final conductor selection should follow applicable codes, approved product data, and qualified engineering review.
Reducing losses
Losses can be reduced by increasing conductor area, shortening the route, raising system voltage, improving power factor, distributing loads differently, or installing parallel conductors where permitted. Larger conductors cost more initially but may reduce annual energy loss. The calculator estimates that cost from operating hours and electricity rate, helping compare capital cost against operating savings.