18 gauge wire at a glance
| Diameter (bare copper) | 0.0403 in (1.02 mm) |
|---|---|
| Cross-section area | 0.82 mm² (1,620 circular mils) |
| Copper ampacity | Not in Table 310.16. NEC 240.4(D) allows 18 AWG on a 7 A overcurrent device |
How far can 18 gauge wire run?
Current is only half the story. The wire loses voltage over distance, and the NEC recommends staying within 3%. This table gives the longest one-way run of 18 AWG copper within 3% drop, by current and voltage.
| Current | 12 V DC | 24 V DC | 120 V AC | 240 V AC |
|---|---|---|---|---|
| 2 A | 11 ft | 23 ft | 113 ft | 226 ft |
| 5 A | 4.5 ft | 9.0 ft | 45 ft | 90 ft |
| 7 A | 3.2 ft | 6.5 ft | 32 ft | 65 ft |
Use the voltage drop calculator for another size, current or limit. For 12 V runs by size, see the 12V wire gauge chart.
What 18 gauge wire is used for
- Thermostat wiring (18/5 is common)
- Doorbells, low-voltage lighting and speaker leads for short runs
- Electronics, LED strips and short 12 V DC runs of a few amps
- Control wiring inside equipment
Cable type and the rules
18 AWG is not building wire for line-voltage branch circuits. It is for low-voltage and electronic wiring. Cables sold as 18 gauge may be solid, stranded or copper-clad, so check the product's ampacity rating, and do not assume a rating from the gauge alone.
Neighboring sizes
| Gauge | Diameter | Copper amps (75°C, with NEC 240.4(D) limits) |
|---|---|---|
| 14 AWG | 0.0641 in | 15 A |
| 16 AWG | 0.0508 in | n/a |
| 18 AWG | 0.0403 in | n/a |
| 20 AWG | 0.0320 in | n/a |
The wire gauge chart covers every size, and the amps per wire size table lists them in all three temperature columns.
Frequently asked questions
How many amps can 18 gauge wire handle?
NEC 240.4(D) limits 18 AWG copper to a 7 A overcurrent device. In low-voltage use, many designers keep it to 5 A or less, especially over longer runs.
Can 18 gauge wire handle 12 volts at 10 amps?
No. 10 A is beyond the 7 A limit and the voltage drop would be extreme. Use at least 14 AWG, and 12 AWG or larger for anything but very short runs.
What is 18 gauge wire used for?
Thermostats, doorbells, low-voltage landscape control, speaker leads and small electronics.
How far can 18 gauge wire run at 12 volts?
About 4.5 feet one way at 5 A within 3% drop, and about 3 feet at 7 A. At 2 A it reaches about 11 feet.