If you are wiring a standard residential branch circuit, the direct answer for wire sizing relies on the 60°C column of the NEC ampacity table for 14, 12, and 10 AWG copper (up to 30A), and the 75°C column for 8 AWG and larger. This rule, dictated by NEC 110.14(C), prevents you from accidentally overloading the relatively lower-temperature terminations found on standard breakers and receptacles.

Getting this wrong means melted insulation, nuisance tripping, or a failed inspection. Below is the definitive reference for sizing copper conductors, complete with the exact temperature columns you need to use, derating mathematics, and a decision tree to lock in your final AWG pick.

How to Read This Copper Wire Amperage Chart

Before looking at the numbers, you must understand the three temperature columns derived from NFPA 70 (NEC) Table 310.16. The ampacity of a wire is not a single fixed number; it changes based on the insulation rating and the termination limits of your devices.

The Golden Rule of Terminations (NEC 110.14(C)): You can only use the ampacity of a wire if every single termination point in that circuit (breaker, lug, receptacle) is rated for that same temperature. Since most standard residential breakers and receptacles are rated for 60°C or 75°C, you must cap your final ampacity at those columns, even if your wire insulation is rated for 90°C.
  • 60°C Column (THW, UF-B, NM-B): Mandatory for circuits 100 amps or less using 14, 12, or 10 AWG wire. Even if you pull 90°C THHN wire, your final legal ampacity for a 12 AWG circuit is capped at the 60°C value (20A).
  • 75°C Column (THHW, XHHW): Used for circuits over 100A, or for 8 AWG and larger wires on circuits 100A or less, provided the terminations are explicitly marked 75°C (which most modern breakers and lugs are).
  • 90°C Column (THHN, XHHW-2): This column is strictly for derating calculations (adjusting for heat and bundling). You cannot use the 90°C ampacity as your final circuit rating unless your terminations are explicitly rated for 90°C, which is virtually nonexistent in residential gear.

The Master Copper Wire Amperage Chart (NEC Table 310.16)

Below is the complete ampacity data for copper conductors in raceway or cable, assuming an ambient temperature of 30°C (86°F).

Bookmark-Friendly Quick-Jump Reference:
For the most common residential circuits, here are your baseline targets before derating:

  • 15 Amps: 14 AWG (60°C Col)
  • 20 Amps: 12 AWG (60°C Col)
  • 30 Amps: 10 AWG (60°C Col)
  • 40 Amps: 8 AWG (75°C Col)
  • 50 Amps: 6 AWG (75°C Col)
  • 60 Amps: 4 AWG (75°C Col)
AWG Size 60°C (140°F)
THW, UF, NM-B		 75°C (167°F)
THWN, XHHW		 90°C (194°F)
THHN, XHHW-2
1415A20A25A
1220A25A30A
1030A35A40A
840A50A55A
655A65A75A
470A85A95A
385A100A115A
295A115A130A
1110A130A145A
1/0125A150A170A
2/0145A175A195A
3/0165A200A225A
4/0195A230A260A

Source: Adapted from NEC Table 310.16 for copper conductors, 30°C ambient. Always verify against the latest adopted NEC edition in your jurisdiction.

Derating: When Your Base Ampacity Drops

The chart above assumes you have no more than three current-carrying conductors in a conduit and an ambient temperature below 86°F (30°C). When you bundle wires together or run them through hot attics, the heat cannot dissipate. NEC 310.15(C)(1) requires you to apply derating factors to prevent the insulation from melting inside the conduit.

The Derating Workflow:

  1. Start with the 90°C column ampacity (this gives you the most thermal headroom for the math).
  2. Multiply by the bundling or temperature correction factor.
  3. Compare the result to the termination temperature limit (usually the 60°C or 75°C column). Your final legal ampacity is the lower of the two numbers.
Worked Example: You are pulling four current-carrying 12 AWG THHN wires through a single conduit for a multi-wire branch circuit.
1. Base 90°C ampacity for 12 AWG = 30A.
2. Derating factor for 4-6 conductors = 80%. (30A × 0.80 = 24A).
3. Termination limit for 12 AWG (60°C column) = 20A.
Result: Because 20A is lower than 24A, your final maximum overcurrent protection is still 20A. The derating didn't force an upsizing here, but if you had 9 conductors in the pipe (50% derating), 30A × 0.50 = 15A. You would be forced to upsize to 10 AWG wire to maintain a 20A circuit.

Decision Tree: Picking the Exact AWG for Your Circuit

Stop guessing. Use this decision-tree-table to lock in the exact copper wire size and breaker pair for standard residential loads. This assumes standard 75°C rated terminations and runs under 75 feet.

If Your Load / Appliance Is... And Your Breaker Is... Buy This Exact Copper Wire (THHN/NM-B) Code Rationale & Notes
Standard 15A Lighting / Receptacles 15 Amp (Single Pole) 14 AWG NEC 240.4(D) strictly limits 14 AWG to 15A, even though 60°C col says 15A. Do not use on 20A breakers.
Kitchen / Bath / Garage Receptacles 20 Amp (Single Pole) 12 AWG NEC 210.11 requires 20A small-appliance circuits. 12 AWG handles the 20A termination limit perfectly.
Electric Dryer / Water Heater 30 Amp (Double Pole) 10 AWG Standard 30A dryer circuits. Use 10/3 NM-B or three strands of 10 AWG THHN in conduit.
EV Charger (Hardwired Level 2) 40 Amp or 50 Amp 8 AWG (40A) or 6 AWG (50A) EV chargers are continuous loads (NEC 625). Wire must be rated 125% of the continuous load. A 40A charger requires 50A wire capacity (6 AWG).
Electric Range / Oven 50 Amp (Double Pole) 6 AWG Standard 50A range circuit. 6 AWG copper at 75°C yields 65A, safely covering the 50A breaker.
100A Subpanel Feeder 100 Amp (Double Pole) 3 AWG 3 AWG copper at 75°C is exactly 100A. Do not use 4 AWG (85A) unless specific load calculations allow it.

What This Chart Cannot Tell You (Voltage Drop & Local Code)

An ampacity chart only tells you the maximum current a wire can carry before its insulation degrades. It does not account for voltage drop over distance. According to OSHA and NEC informational notes, keeping voltage drop below 3% for branch circuits and 5% overall ensures equipment operates efficiently and prevents motor burnout.

The Voltage Drop Trap:
Imagine you are wiring a 120V, 30A RV receptacle located 100 feet from the main panel. The chart says 10 AWG copper is legal for 30A. However, using the standard voltage drop formula VD = (2 × K × I × L) / CM (where K=12.9 for copper, I=30A, L=100ft, and CM=10,380 for 10 AWG):

  • VD = (2 × 12.9 × 30 × 100) / 10,380 = 7.45 Volts.
  • 7.45V / 120V = 6.2% drop. This is double the recommended 3% limit.

To fix this, you must ignore the base chart and upsize to 6 AWG copper (CM = 26,240), which drops the loss to 2.94V (2.45%), safely under the 3% threshold.

Final Default Recommendation: If your one-way wire run exceeds 75 feet, abandon the base ampacity chart and run a voltage drop calculation first; always size the wire to satisfy the voltage drop requirement, then verify it exceeds the breaker ampacity. Finally, always size your breaker to the lowest temperature rating of any device in the circuit chain, and defer to your local Authority Having Jurisdiction (AHJ) if municipal amendments override baseline NEC tables.