⚡ Engineering

Wire Gauge Calculator 2026 — AWG & Voltage Drop

Wire gauge (AWG) and voltage drop calculator — enter current draw, wire length, and source voltage to find the required AWG size and actual voltage drop using NEC guidelines.

Current (Amps) Please enter a positive current value.

One-Way Length (Feet) Please enter a positive wire length.

Source Voltage (V) Please enter a valid voltage.

Max Voltage Drop (%)

Wire Material

Circuit Type

Wire Gauge Results

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Recommended AWG

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Voltage Drop

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Drop %

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Wire Resistance

How It Works

Enter current and wire length — input the load current in amps and the one-way distance from power source to device in feet.
Set voltage and maximum drop — choose your source voltage (typically 120V or 240V in the US) and your allowed voltage drop (NEC recommends 3% for branch circuits).
Get the recommended AWG — the calculator finds the smallest AWG wire that keeps voltage drop within your limit, and shows the actual voltage drop in volts and percentage.

The wire gauge calculator uses resistance-per-foot values from the NEC Chapter 9 Table 9 to compute voltage drop as VD = 2 × K × I × L / CM (for single-phase), where K is the resistivity constant (12.9 for copper, 21.2 for aluminum), I is current in amps, and L is one-way length in feet. It then selects the minimum AWG that satisfies the maximum voltage drop constraint.

Understanding AWG Wire Sizing and Voltage Drop

Selecting the correct wire gauge is critical for both safety and performance in electrical installations. An undersized wire overheats under load, creating a fire hazard, while also causing excessive voltage drop that starves your equipment of the voltage it needs to operate properly.

NEC Voltage Drop Guidelines

The National Electrical Code (NEC) recommends keeping voltage drop to 3% or less for branch circuits and feeders individually, and no more than 5% combined. These are recommendations, not hard requirements — but following them ensures equipment operates within its rated voltage range and prolongs its service life. For sensitive electronics, motor loads, and LED drivers, staying under 2% is best practice. Use this tool alongside our Ohm's Law Calculator for complete circuit analysis.

AWG	Copper Resistance (Ω/1000ft)	Ampacity (60°C)	Common Use
14	2.525	15 A	General lighting / 15A circuits
12	1.588	20 A	Kitchen, bath / 20A circuits
10	0.999	30 A	Dryers, A/C / 30A circuits
8	0.628	40 A	Electric ranges / 40A circuits
6	0.395	55 A	Sub-panels / 55A circuits
4	0.249	70 A	Large sub-panels / EV chargers
2	0.156	95 A	Service entrance / large feeders

Copper vs Aluminum Wiring

Aluminum wire has about 61% of the conductivity of copper, meaning you need a larger diameter (lower AWG number) to carry the same current with the same voltage drop. Aluminum is commonly used for service entrance conductors and large feeder runs because it is significantly lighter and less expensive per foot than copper. For branch circuit wiring inside walls, copper remains the standard due to its superior conductivity, easier terminations, and safety track record. Use the material selector in our wire gauge calculator to switch between copper and aluminum calculations. Also see the Voltage Divider Calculator for related circuit design work.

Frequently Asked Questions

What is the NEC recommended maximum voltage drop?

The National Electrical Code (NEC) recommends a maximum voltage drop of 3% for branch circuits and feeder circuits individually, and no more than 5% total from the service entrance to the final outlet. For sensitive electronics and long runs, keeping voltage drop under 2% is generally recommended.

How does wire length affect AWG selection?

Voltage drop increases with wire length because resistance is proportional to length. For longer runs, you must use a heavier (lower AWG number) wire to keep voltage drop within acceptable limits, even if the current draw is the same. Doubling the wire length roughly doubles the voltage drop for the same gauge.

What is the difference between AWG and circular mils?

AWG (American Wire Gauge) is a standardized wire gauge system used primarily in North America. A lower AWG number means a thicker wire. Circular mils (CM) measure the cross-sectional area of a wire; 1 CM equals the area of a circle with a 0.001-inch diameter. Larger CM values indicate thicker wires with lower resistance.

What AWG wire should I use for a 20-amp circuit?

For a standard 20-amp 120V branch circuit in the US, the NEC requires a minimum of 12 AWG copper wire. However, if the run is long (over 50-75 feet), you may need to upsize to 10 AWG to keep voltage drop within the 3% NEC recommendation. Always verify with a licensed electrician for final installations.