Lookup current capacity by wire size for copper & aluminum conductors. Based on NEC Table 310.16 with derating and ambient temperature corrections.
Base Ampacity
—
from NEC 310.16
Derating Factor
100%
conductors in raceway
Ambient Correction
100%
temperature factor
Final Ampacity
—
amps continuous safe load
Max Continuous Load (80%)
—
for 3+ hr loads
Recommended Breaker
—
standard size
Typical Circuit
—
at 120V / 240V
NEC 310.16 Ampacity Reference Table
Base ampacity values (amps) for copper and aluminum at 60°C / 75°C / 90°C. Highlighted row is your selected size.
AWG / kcmil
60°C
75°C
90°C
Frequently Asked Questions
What size wire do I need for 100 amps?▼
For a 100 amp circuit, you generally need a 3 AWG copper wire (rated 100A at 75°C) or a 1 AWG aluminum wire (rated 100A at 75°C) per NEC Table 310.16. If the circuit uses 90°C insulation like THHN, a 4 AWG copper is also acceptable for the conductor rating, but the termination is usually rated 75°C so sizing must follow the 75°C column.
How is cable ampacity determined?▼
Cable ampacity is determined by the conductor size (AWG or kcmil), material (copper or aluminum), insulation temperature rating (60°C, 75°C, or 90°C), and is then corrected for ambient temperature and the number of current-carrying conductors in a raceway or cable. NEC Table 310.16 provides the base values, with correction factors in Tables 310.15(B)(1) and 310.15(C)(1).
Does aluminum wire have the same ampacity as copper wire?▼
No. Aluminum has roughly 61% of the conductivity of copper, so aluminum conductors must be sized about one or two AWG sizes larger than copper for the same ampacity. For example, 6 AWG copper and 4 AWG aluminum both carry 55A at 75°C, while 2 AWG copper and 1/0 AWG aluminum both carry approximately 115–120A at 75°C.
⚠️ This tool is for reference and educational use. Always consult a licensed electrician and verify local electrical codes before installation.