Whether you’re installing, extending, or rewiring a circuit, finding out the wire gauge and amperage you will need is a key first step. The gauge—or size—of the wire used needs to match amperage rating (energy level) of the circuit. The higher the amperage rating, the larger the electrical wires need to be to avoid generating excess heat that can cause melted wires and even electrical fires.
Knowing how much energy your new lighting fixture, appliance, or heater will need, the type of wire your home currently uses when rewiring, and using an electrical wire size chart to ensure you have the right materials will all ensure your electrical project goes safely and smoothly, both in the short and long-term.
Why Wire Gauge Is Important
Safety risks come into play any time a device or appliance tries to draw more power on a circuit than the wire gauge is rated for, and one of the most common causes of household electrical fires is overloading an extension cord by plugging in a heater—or too many chargers.
A typical extension cord wire is a 16-gauge, meant for everyday chargers and lamps of up to 15-amp, but a heater needs that full capacity on its own— and oftentimes more. So if you’re in need of extra outlets, make sure you’re plugging heaters directly into the wall, or are picking up a heavy-duty extension cord for your home.
Circuit breakers or wiring fuses do offer some protection against overloading and overheating, but they shouldn’t be your absolute go-to. Both are designed to sense current overloads and to trip or “blow” before the wires reach the danger point. Nothing is foolproof though, so it’s still important to avoid plugging too many appliances into a circuit and stay below the amperage rating.
| Wire Use | Rated Ampacity | Wire Gauge |
|---|---|---|
| Low-voltage lighting and lamp cords | 10 amps | 18-gauge |
| Extension cords (light-duty) | 13 amps | 16-gauge |
| Light fixtures, lamps, lighting circuits | 15 amps | 14-gauge |
| Kitchen, bathroom, and outdoor receptacles (outlets); 120-volt air conditioners | 20 amps | 12-gauge |
| Electric clothes dryers, 240-volt window air conditioners, electric water heaters, sometimes cooktops and wall ovens | 30 amps | 10-gauge |
| Cooktops and ranges | 40-50 amps | 6-gauge |
| Electric furnaces, large electric heaters | 60 amps | 4-gauge |
How to Use a Wire Gauge Chart
You can determine the ampacity of wires you have on hand, and the gauge—or diameter—of wires needed for your project with a wire gauge chart. When purchasing wire, you’ll see a few different numbers on the packaging or product description.
The number followed by AWG, short for American Wire Gauge, is the gauge of the entire wire. This number takes into account any smaller wires woven together within the insulation. Any numbers after AWG indicate how many strands of smaller wire are used, and the gauge of each.
If a spool of wire is only labeled with a set of numbers (for example, 10/3), there are three separate 10-gauge strands within the wire that can be used for connecting, plus a grounding wire.
If you’re buying wires by size in inches or millimeters, or have stripped and measured uninsulated wires with a gauge tool, you can also use a wire gauge chart to determine the maximum amperage of a wire. Most charts provide ampacity for copper and aluminum wire and their most common insulation materials.
How Wires Are Sized
If you’ve shopped for electrical wire, you have likely noticed that there are many types and sizes of electrical wire to choose from. Different types of wire are intended for different uses, but with any of these wire types, knowing the right wire size, or wire gauge, determines amps, which is the key to making the right choice.
Wire is sized by the American Wire Gauge (AWG) system. Wire gauge refers to the physical size of the wire, rated with a numerical designation that runs opposite to the diameter of the conductors—in other words, the smaller the wire gauge number, the larger the wire diameter. Common sizes include 16-, 14-, 12-, 10-, 8-, 6-, and 2-gauge wire. The size of the wire dictates how much current can safely pass through the wire.
Electrical current is measured in amps, and each wire gauge has a maximum safe carrying capacity. For standard non-metallic (NM) copper cable, these amperage and wire gauge capacities help you to calculate what size wire you need:
| Amperage Capacities for Standard Non-Metallic (NM) Cable | |
|---|---|
| 16-gauge wire | 13 amps |
| 14-gauge wire | 15 amps |
| 12-gauge wire | 20 amps |
| 10-gauge wire | 30 amps |
| 8-gauge wire | 40 amps |
| 6-gauge wire | 55 amps |
| 4-gauge wire | 70 amps |
| 3-gauge wire | 85 amps |
| 2-gauge wire | 95 amps |
Copper vs. Aluminum Wiring
This electrical wire size chart is the place to start when working with copper wires, but it’s important to keep in mind aluminum wires may also be present in your space.
Aluminum wire is more typically used for fixed wiring in the 1960s and 70s to keep costs low when building homes. However, it also has a lower amperage capacity than copper, the wire need to be thicker to carry the same current, and and it tends to expand when it heats up, which can cause connection issues and fire safety concerns over time.
Although it’s more expensive than aluminum, copper wire is now the preferred material in homes, thanks to the strength, durability, and higher conductivity.
Stranded vs. Solid Wire
It’s also important to purchase the style of wire that best fits your needs. Stranded wire is made up of multiple small strands woven together within insulation and tends to be more flexible, making it ideal for smaller areas. However, it’s also prone to fraying and more susceptible to damage.
Solid wire, on the other hand, is made of a single solid copper conductor. It tends to be much easier to secure in standard switches and receptacles, and is best used for rewiring and installation projects needing a higher ampacity.
FAQ
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Outlets, light fixtures, and air conditioners are typically wired with 14 or 12-gauge wire, and appliances like stoves, heaters, and laundry machines use 10 to 6-gauge wire.
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An 8-gauge wire is larger than a 14-gauge wire, at 0.1285 inches in diameter compared to 0.0641. This is because in the AWG system, the thicker a wire is, the lower the gauge number.
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A 6-gauge wire can carry 50 amps about 182 feet for copper wire, and 114 feet for aluminum. Using too long of a wire between a source and a load leads to voltage drop, which is can cause issues for the appliances being powered.
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