18 Gauge Wire (18/2 Wire, 18/3 Wire, 18/4 Wire) Amps: Guide to 18 Gauge Copper Speaker Wire
18 gauge wires are commonly used for powering devices that don't require too strong currents, including home or car speakers, except subwoofers.
But, for many other applications, 18 gauge wires tend to be too thin, especially when powering home appliances, tools, and similar loads.
Published: December 27, 2022.
18 Gauge Wire Thickness/Dimensions
AWG 18 wire or 18 gauge wire features physical dimensions of:
- diameter: 1.0237 mm, 0.0403 inches,
- cross-section area: 0.8230 mm2, 0.0013 inches2,
These values are for solid 18 gauge wires, while 18 gauge stranded wires feature somewhat different values - due to the air gaps between the wire strands, 18 gauge stranded wire feature a 12-14% larger diameter (instead of 1.0237 mm, stranded 18 gauge wire feature diameter of ~1.15 mm, which is practically negligible).
18 Gauge Wire Materials
Most common 18 gauge wire materials include:
- Copper: both solid and stranded copper wires are commonly used for various applications, including audio/speaker wires, LED lights, alarms, and similar applications that really don't require strong currents.
- Oxygen-Free Copper (OFC): 18 gauge OFC wires are used practically only for speaker wires - they offer somewhat lower resistance than "common" copper wires at a somewhat higher price.
- Tinned Stranded Copper 18 gauge wires feature numerous tinned copper strands, offering very high corrosion resistance. As such, Tinned Stranded Copper 18 gauge wires are commonly used in automotive, marine, and electrical applications requiring thinner wires but with exceptional corrosion resistance.
- Aluminum and Copper Clad Aluminum (CCA) 18 gauge wires are lighter than copper wires but feature higher resistance and are rarely used since 18 gauge copper wires are already rather light and easy to work with.
- Silver 18 gauge wires are used for high-quality audio systems and for low-power speakers. Since they are made of silver, these wires are more expensive than copper wires.
- Gold is not used for making wires since it has higher resistance than silver. But, gold-plated connectors ensure reliable contacts after years of use.
18 Gauge Wire Ampacity
The most important feature of any wire is its Ampacity (current load-carrying ability), which is given in Amps at certain temperatures.
The default Ampacity of 18 gauge solid copper wire is:
- @60°C/140°F: 10 Amps,
- @75°C/167°F: 14 Amps,
- @90°C/194°F: 16 Amps.
As one can see, for applications when the maximum allowed wire surface temperature is 60°C/140°F, the default/theoretical Ampacity of the 18 gauge copper wire is "just" 10 Amps.
For more information about Ampacities of other wires sizes, feel free to check our AWG to mm2 Conversion Chart and Wire Sizes article.
However, these values are just default values. To increase safety, the 80% Rule should be used - thus, the actual Ampacity of 18 gauge wire is:
- @60°C/140°F: 10 Amps * 0.8 = 8 Amps
- @75°C/167°F: 14 Amps * 0.8 = 11.2 Amps
- @90°C/194°F: 16 Amps * 0.8 = 12.8 Amps
As one can see, for most applications, the Ampacity of the 18 gauge wire is - 8 Amps. And this is without taking into account cable length.
10%/50 Feet Rule
When longer wires are used, the Ampacity is decreased by 10% for every 50 feet (~15m) of the wire length.
Thus, when calculating the Ampacity for 18 gauge copper wire @60°F/140°F, we can write:
- 18 Gauge 50 Feet Wire Ampacity = 10 * 0.8 / 1.1 = ~7.272 Amps,
- 18 Gauge 100 Feet Wire Ampacity = 10 * 0.8 / 1.2 = ~6.666 Amps,
- 18 Gauge 150 Feet Wire Ampacity = 10 * 0.8 / 1.3 = ~6.153 Amps,
- 18 Gauge 200 Feet Wire Ampacity = 10 * 0.8 / 1.4 = ~5.714 Amps.
For short, if You are using an 18 gauge speaker wire, an 18-gauge wire is good enough for 50 Watts @4Ω (up to 50 feet/15 m) and for 100 Watts @8Ω (up to 100 feet/30 m). For stronger systems, consider 16-gauge or even 14-gauge wires.
18 Gauge Wire Cables: 18/2 Wire, 18/3 Wire, and 18/4 Wire
Each cable consists of 2 to 4, rarely more, wires bundled together, where the number of wires may vary depending on the intended cable use.
Thus, the cables are labeled as 18/2 Wire (or "18 2 Wire"), 18/3 Wire (18 3 Wire), and 18/4 Wire (18 4 Wire).
When the cable is labeled as, for example, "18/3 Wire", that means that it is a cable consisting of three 18 gauge wire conductors and one ground wire. Thus:
- 18/2 Wire (18 2 Wire) consists of two 18 gauge wire conductors and one ground wire.
- 18/3 Wire (18 3 Wire) consists of three 18 gauge wire conductors and one ground wire.
- 18/4 Wire (18 4 Wire) consists of four 18 gauge wire conductors and one ground wire.
In order to help the user properly connect the wires, they are color-coded - the actual color codes depend on the intended wire/cable use, but also the country.
These 18 gauge cables are intended for AC applications, thus the 18/2 cable features three wires, including phase, neutral, and ground.
For DC applications, many manufacturers label their wires as:
- 18 gauge 2 conductor wire: two 18 gauge wires,
- 18 gauge 3 conductor wire: three 18 gauge wires,
- 18 gauge 4 conductor wire: four 18 gauge wires.
And best of all, some manufacturers even mix these labels and sometimes even write "18/2 Wire" and "18 Gauge 2 Conductor Wire" (which is obviously incorrect) on the same package.
Personally, when buying the wires/cables in the local hardware store or online shops, always be sure to check the number of wires and the thickness of each wire.
Long Story Short: 18 gauge wires are relatively thin and cheap, even high-quality OFC solid/stranded wires. For wires that must feature excellent corrosion resistance, go for Tinned Stranded Copper wires.
And whatever You do, stay safe - it is your own responsibility, after all ... If unsure, contact a local certified electrician and let him/her do the work ...