Voltage Drop Calculator (Residential)

Calculate voltage drop for residential wiring and check compliance with the NEC 3% recommendation.

About this calculator

This calculator estimates voltage drop over a residential branch circuit and checks it against the 3% voltage-drop recommendation in NFPA 70, the National Electrical Code (NEC), for normal operation. Wire Gauge (AWG) outweighs every other input in the result: the resistance table behind this calculator runs from 2.525 ohms per 1,000 ft for thin 14 AWG wire down to 0.0983 ohms per 1,000 ft for heavy 1/0 AWG wire -- a swing more than 25 times larger than what a realistic change in One-Way Distance or Current produces on its own. Distance and Current both move Voltage Drop and Drop Percentage in direct proportion (double either one and voltage drop doubles), but neither comes close to the swing you get from choosing a heavier gauge.

System Voltage doesn't affect Voltage Drop or Power Loss at all -- it only changes the percentage the drop represents and the voltage that actually reaches the load, since a 3-volt drop is a much bigger share of 120V than of 240V. At the calculator's defaults (75 ft, 15A, 12 AWG, 120V), the circuit sits right at the edge of NEC compliance -- around 75-76 ft one-way is roughly where this exact combination crosses the 3% threshold.

Inputs

Wire Gauge (AWG)

One-Way Distance

Current

System Voltage

Tab to move between fields

Results

Voltage Drop

3.57 V

Drop Percentage2.98%

Voltage at Load116.43 V

NEC 3% Compliant1

Power Loss53.6 W

Figures current as of 2023. Source: NFPA 70, National Electrical Code (NEC), 2023 edition

How to Use This Calculator

Select Wire Gauge (AWG) from the dropdown — lower AWG = thicker wire.
Enter One-Way Distance (ft) from panel to load.
Input Current (amps) drawn by the load.
Review Actual Voltage Drop (%) — NEC recommends keeping this below 3% for branch circuits.
If voltage drop exceeds 3%, select the next heavier AWG and recalculate.

How the result changes with One-Way Distance

One-Way Distance	Voltage Drop
38	1.81 V
56	2.67 V
113	5.38 V
188	8.96 V

What each input means

Wire Gauge (AWG): AWG wire gauge of the installed or planned conductor.
One-Way Distance: One-way distance from panel to the load in feet.
Current: Current draw of the circuit load in amps.
System Voltage: Nominal system voltage of the circuit.

How this is calculated

Worked example, using the default values

Identify Input Parameters
4 parameters
Wire Gauge (AWG) = 12, One-Way Distance = 75, Current = 15, System Voltage = 120 = 4 input(s) provided
Calculate Voltage Drop
Voltage Drop
3.57 = 3.57
Calculate Drop Percentage
Drop Percentage
2.98 = 2.98
Calculate Voltage at Load
Voltage at Load
116.43 = 116.43

Figures and sources

3% recommended voltage drop for branch circuits (2023) — NFPA 70, National Electrical Code (NEC), 2023 edition

Engine last updated September 2, 2026. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.

Frequently Asked Questions

Why does wire gauge matter more than distance or current?

Wire Gauge sets the resistance per foot used in the voltage drop formula, and the table behind this calculator spans a roughly 25-to-1 range from 14 AWG to 1/0 AWG -- a much bigger swing than a realistic change in One-Way Distance or Current produces, which is why gauge dominates both Voltage Drop and Drop Percentage.

Does the system voltage (120V vs 240V) change how much voltage I lose?

No -- Voltage Drop in volts and Power Loss in watts depend only on Wire Gauge, One-Way Distance, and Current, not on System Voltage. What changes is Drop Percentage, since the same volt drop is a larger share of a 120V circuit than of a 240V circuit.

At what distance does the default circuit stop meeting the NEC 3% guideline?

With the calculator's default 12 AWG wire and 15A load, the one-way distance from panel to load crosses the 3% voltage-drop recommendation set out in NFPA 70, the National Electrical Code (NEC), at right around 75 to 76 feet -- meaning the calculator's own default inputs sit almost exactly on that line.

How does doubling the current draw affect voltage drop?

Voltage Drop is directly proportional to Current in this calculator's formula, so doubling the amperage on a circuit roughly doubles the calculated Voltage Drop and Drop Percentage for the same wire gauge and distance, though the exact figure also depends on the resistance of the gauge selected.

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