AWG stands for American Wire Gauge. Lower numbers mean thicker wire. A 10 AWG cord handles more current than a 16 AWG cord. Extension cords are most commonly 16, 14, 12, or 10 AWG.

Why does cord length affect the gauge I need?

Longer cords have more resistance, which causes a larger voltage drop at the outlet end. To keep voltage drop below 5%, you need thicker wire for longer runs.

Can I use a 16 AWG cord for a 15-amp circuit?

Only if the connected load is light (up to 10–13 A max). A 16 AWG cord cannot safely carry a full 15 A load at any distance. For an actual 15 A load, use at least a 14 AWG cord for short runs or 12 AWG for longer distances.

What is the maximum length for a 12 AWG extension cord?

At 15 A on 120 V, a 12 AWG cord keeps voltage drop under 5% up to roughly 100 feet. Beyond that, use 10 AWG or run a permanent circuit.

Does this tool apply to outdoor extension cords?

Yes — gauge requirements are the same outdoors. Make sure the cord is also rated for outdoor use (look for "W" in the jacket marking, e.g. SJTW).

What voltage drop percentage is acceptable?

The NEC recommends no more than 5% voltage drop for branch circuits and feeders combined. Most extension cord charts target 3–5%. Motor loads are especially sensitive to low voltage.

Extension Cord Gauge Selector

Enter load amps and cord length to estimate an AWG gauge within this tool's 30 A range. Use a listed cord rated for the load and follow the manufacturer and local electrical requirements.

Cord Parameters

Voltage

Load (amps) — total draw of all devices on this cord

Tip: check the nameplate on your device for amps or watts ÷ volts.

Cord length (feet)

Enter your parameters and click Calculate.

Common Extension Cord Gauge Reference (120 V, ≤5% voltage drop)

AWG	Max amps	Up to 25 ft	Up to 50 ft	Up to 100 ft	Up to 150 ft
16 AWG	13 A	OK	OK (<10 A)	Oversize needed	Oversize needed
14 AWG	15 A	OK	OK	OK (<13 A)	Oversize needed
12 AWG	20 A	OK	OK	OK	OK (<15 A)
10 AWG	30 A	OK	OK	OK	OK

Summary

Choosing the wrong gauge for an extension cord can cause dangerous voltage drop, overheating, and fire. This tool estimates gauge and voltage drop for listed cords up to 30 A. It does not replace the cord manufacturer's rating, applicable code, or review by a qualified electrician; never exceed a cord, plug, receptacle, or circuit rating.

How it works

Enter the total load in amps drawn by your device or devices.
Enter the total extension cord length in feet (one-way, not round trip).
Choose 120 V or 240 V service.
The tool looks up the minimum AWG from NEC-aligned extension cord tables.
A result card shows the recommended gauge, max safe ampacity, and a voltage-drop estimate.

Use cases

Safely powering power tools and shop equipment.
Running space heaters or window AC units on a long cord.
Outdoor lighting and holiday decorations.
Generator hook-up cords for emergency power.
RV and camping power leads.
Temporary construction site wiring.

Frequently Asked Questions

Last updated: 2026-06-15 · Reviewed by Nham Vu