Wire Gauge Ampacity Calculator
Selecting the correct wire gauge for a circuit is a safety-critical decision governed by NEC Table 310.16. This table lists the ampacity (maximum safe current-carrying capacity) for copper and aluminum conductors at three temperature ratings: 60 C, 75 C, and 90 C. Most residential wiring terminations are rated for 60 C or 75 C, so the lower rating applies even if the wire insulation is rated higher. This calculator looks up the NEC Table 310.16 ampacity for the selected gauge, material, and temperature column, and also computes the 80% continuous load limit.
NEC ampacity lookup method
Ampacity = NEC Table 310.16 value for AWG, material, temperature column
Max continuous load = Ampacity × 0.80 (NEC 210.19 continuous load rule)
NEC Table 310.16 assumes not more than three current-carrying conductors in a raceway, cable, or earth at an ambient temperature of 30 C (86 F). Derating is required for higher conductor counts (NEC Table 310.15(C)(1)) or higher ambient temperatures (NEC Table 310.15(B)(1)(a)). Always verify with the current edition of the NEC adopted in your jurisdiction.
Common wire gauge applications
- 14 AWG copper (60 C: 15A): general lighting and receptacle circuits on 15A breakers.
- 12 AWG copper (60 C: 20A): kitchen, bathroom, and garage receptacles on 20A breakers.
- 10 AWG copper (60 C: 30A): electric dryers, air conditioners, water heaters on 30A breakers.
- 8 AWG copper (60 C: 40A): electric ranges and large HVAC compressors on 40A breakers.
- 6 AWG copper (60 C: 55A): subpanel feeders and large air conditioners.
- Aluminum is commonly used for service entrance and feeder conductors 1 AWG and larger.
Wire gauge ampacity: frequently asked questions
What is ampacity and why does it matter?
Ampacity is the maximum current a conductor can carry continuously without exceeding its temperature rating. If a wire carries more current than its ampacity, it overheats, which can melt insulation and cause a fire. Matching wire gauge to load and breaker size is a fundamental NEC requirement.
What is the difference between AWG gauges?
AWG (American Wire Gauge) is an inverse scale: smaller numbers mean larger wire. 14 AWG is smaller than 12 AWG, which is smaller than 10 AWG. Each 3-gauge decrease roughly doubles the cross-sectional area, and ampacity increases correspondingly. Common residential gauges are 14 AWG (15A), 12 AWG (20A), and 10 AWG (30A).
When do I use aluminum wire instead of copper?
Aluminum wire is lighter and less expensive per foot than copper and is commonly used for service entrance conductors and large feeder circuits (100A panels, range circuits). However, aluminum requires special connectors rated for aluminum (AL/CU), and the NEC requires specific terminations at devices. Never use aluminum for 15A or 20A branch circuits.
What is the 80% NEC continuous load rule?
For continuous loads (operating more than 3 hours), NEC 210.19 and 215.2 require the conductor ampacity to be at least 125% of the continuous load. Equivalently, the maximum continuous load on a conductor is 80% of its ampacity. A 20A circuit with 12 AWG wire should not carry more than 16A of continuous load.
Does conduit fill or bundling reduce ampacity?
Yes. When more than 3 current-carrying conductors are bundled in the same conduit or raceway, NEC Table 310.15(C)(1) requires ampacity derating. For 4 to 6 conductors, multiply ampacity by 0.80; for 7 to 9 conductors, by 0.70. High ambient temperatures also require derating per NEC Table 310.15(B)(1).
Official sources
- NFPA 70 (NEC): National Electrical Code Table 310.16.
- U.S. DOE: Home Electrical Systems.
Reviewed by the CalculatorHub team, edited by James Graham, 15 June 2026. See our methodology.