What formula does the Voltage Drop Calculator use?

For DC and single-phase circuits it uses drop = 2 x length x current x (resistivity / conductor area), doubling the length to account for the return conductor. For three-phase circuits it replaces the factor of 2 with the square root of 3, matching standard line-to-line drop formulas.

Does the Voltage Drop Calculator support AWG wire gauges?

Yes. Pick any standard AWG size from 20 gauge up to 4/0, and the calculator derives the conductor's cross-sectional area from the standard AWG diameter formula before computing resistance.

Why does aluminum wire show more voltage drop than copper?

Aluminum has higher electrical resistivity than copper, so for the same gauge and length an aluminum conductor drops more voltage carrying the same current — this calculator models that difference directly.

Is the Voltage Drop Calculator accurate enough for electrical code compliance?

It gives a nominal-temperature estimate useful for sizing decisions, but it is not a substitute for the resistance tables and temperature corrections in your local electrical code. Verify important wire sizing with a qualified electrician.

Can I calculate voltage drop for a solar or DC battery wiring run?

Yes, select DC as the phase — the calculator applies the same doubled-length formula used for single-phase AC, which is correct for a two-conductor DC circuit.

Does the Voltage Drop Calculator work in feet as well as meters?

Yes, use the length unit toggle to switch between meters and feet; the calculator converts your entry internally before computing the drop.

Voltage Drop Calculator Online

Estimate voltage drop over a copper or aluminum wire run from gauge, length, and current, right in your browser.

Your wire gauge, length, current, and voltage figures are calculated locally in your browser and are never uploaded anywhere.

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About Voltage Drop Calculator

The Voltage Drop Calculator estimates how much voltage a wire run loses between the source and the load, based on conductor material, AWG gauge, one-way run length, load current, and system voltage. It supports copper and aluminum conductors, DC, single-phase, and three-phase circuits, and switches between meters and feet for the run length. The result shows the voltage drop in volts and as a percent of system voltage, plus the end voltage the load actually sees. It is useful for sizing extension cords, panel feeders, solar array wiring, or any long branch circuit where a thin gauge or a long run can starve equipment of voltage. This is an engineering estimate, not a code compliance tool — verify wire size against the applicable electrical code before ordering wire or wiring a circuit. Everything runs locally in your browser.

Features

Solves voltage drop for copper or aluminum conductors
Covers the full common AWG range from 20 gauge to 4/0
DC, single-phase AC, and three-phase AC circuit modes
Switch the run length between meters and feet
Shows drop in volts, drop as a percent, and the end voltage at the load
Copy a plain-text summary of every input and result
Instant recalculation as you change any field
Runs entirely in your browser with no circuit data sent anywhere

How to use the Voltage Drop Calculator

Pick copper or aluminum as the conductor material
Choose the wire gauge (AWG) from the dropdown
Enter the one-way run length, load current, and system voltage
Select DC, single-phase, or three-phase to match the circuit
Read the estimated voltage drop, drop percent, and end voltage

Example

Input

12 AWG Cu, 30 m, 15 A, 120 V

Output

Drop: ~4.7 V (3.9%)

A 30 m run of 12 AWG copper carrying 15 A on a 120 V circuit loses about 3.9% of the supply voltage.

Common errors & troubleshooting

The voltage drop looks far too small. — Make sure you entered the one-way run length, not the round trip — the calculator already accounts for the return conductor on DC and single-phase circuits.
Copper and aluminum give the same drop. — Confirm the material toggle is actually set to Aluminum; aluminum has roughly 1.6x the resistance of copper at the same gauge.
Feet and meters give inconsistent results after switching units. — Re-enter the length value after switching units — the field holds a raw number that is interpreted in whichever unit is currently selected.
Three-phase drop looks lower than expected compared to single-phase. — That is expected: three-phase drop uses a sqrt(3) factor instead of the doubled conductor length used for DC and single-phase runs.

Frequently asked questions

What formula does the Voltage Drop Calculator use?: For DC and single-phase circuits it uses drop = 2 x length x current x (resistivity / conductor area), doubling the length to account for the return conductor. For three-phase circuits it replaces the factor of 2 with the square root of 3, matching standard line-to-line drop formulas.
Does the Voltage Drop Calculator support AWG wire gauges?: Yes. Pick any standard AWG size from 20 gauge up to 4/0, and the calculator derives the conductor's cross-sectional area from the standard AWG diameter formula before computing resistance.
Why does aluminum wire show more voltage drop than copper?: Aluminum has higher electrical resistivity than copper, so for the same gauge and length an aluminum conductor drops more voltage carrying the same current — this calculator models that difference directly.
Is the Voltage Drop Calculator accurate enough for electrical code compliance?: It gives a nominal-temperature estimate useful for sizing decisions, but it is not a substitute for the resistance tables and temperature corrections in your local electrical code. Verify important wire sizing with a qualified electrician.
Can I calculate voltage drop for a solar or DC battery wiring run?: Yes, select DC as the phase — the calculator applies the same doubled-length formula used for single-phase AC, which is correct for a two-conductor DC circuit.
Does the Voltage Drop Calculator work in feet as well as meters?: Yes, use the length unit toggle to switch between meters and feet; the calculator converts your entry internally before computing the drop.

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