For a standard 15A residential lighting circuit, you need 14 AWG copper wire. For a 20A receptacle circuit, step up to 12 AWG copper. For a 50A EV charger or range, use 6 AWG copper or 4 AWG aluminum. Sizing wire isn't just about matching a number to a breaker; it requires understanding temperature ratings, insulation types, and conduit fill. This guide provides the exact data you need to make a definitive pick without a second trip to the electrical supply house.

MAINS VOLTAGE WARNING: Any work involving your electrical panel or branch circuits exposes you to lethal voltage. Always de-energize the main breaker, lock/tag out if possible, and verify the circuit is dead with a tested CAT III or CAT IV multimeter. NEC-style guidance provided here is for educational purposes; your local Authority Having Jurisdiction (AHJ) has final authority, and local code may require a licensed electrician for panel and feeder work.

How to Read This Amperage Wire Gauge Chart

The data below is sourced directly from NFPA 70: National Electrical Code (NEC) Table 310.16. This table assumes an ambient air temperature of 30°C (86°F) and a maximum of three current-carrying conductors bundled in a raceway or cable. The columns are split by conductor material (Copper vs. Aluminum) and the temperature rating of the wire insulation and termination points (60°C, 75°C, and 90°C). Use the quick-jump links below to find the most common residential circuit sizes.

The Complete Amperage Wire Gauge Chart

AWG / kcmil Copper 60°C (140°F) Copper 75°C (167°F) Copper 90°C (194°F) Aluminum 60°C (140°F) Aluminum 75°C (167°F) Aluminum 90°C (194°F)
14 AWG15A20A25A———
12 AWG20A25A30A15A20A25A
10 AWG30A35A40A25A30A40A
8 AWG40A50A55A30A40A45A
6 AWG55A65A75A40A50A60A
4 AWG70A85A95A55A65A75A
3 AWG85A100A115A65A75A85A
2 AWG95A115A130A75A90A100A
1 AWG110A130A145A85A100A115A
1/0 AWG125A150A170A100A120A135A
2/0 AWG145A175A195A115A135A150A
3/0 AWG165A200A225A130A155A175A
4/0 AWG195A230A260A150A180A205A
Quick Reference: 15A Circuit — Use 14 AWG Copper (60°C col) or 12 AWG Aluminum (60°C col).
Quick Reference: 20A Circuit — Use 12 AWG Copper (60°C col) or 10 AWG Aluminum (75°C col).
Quick Reference: 50A Circuit — Use 6 AWG Copper (75°C col) or 4 AWG Aluminum (75°C col).
Quick Reference: 100A Feeder — Use 3 AWG Copper (75°C col) or 1 AWG Aluminum (75°C col).

Which Temperature Column Applies to Your Install?

The most common mistake DIYers make is reading the 90°C column because THHN wire is rated for 90°C. Do not use the 90°C column for final breaker sizing. According to NEC 110.14(C), your allowable ampacity is limited by the lowest temperature rating of any connected component, including the breaker lugs, terminal bars, and the wire insulation itself.

The 60°C Rule for Residential: For circuits rated 100A or less, standard breakers and lugs are tested and rated at 60°C unless explicitly marked otherwise. Furthermore, standard NM-B (Romex) cable is strictly limited to the 60°C column, regardless of the fact that the individual wires inside it might have 90°C printed on the jacket. If you are pulling NM-B, or using THHN in conduit on a standard 20A, 30A, or 50A breaker, use the 60°C column.

Use the 75°C column only when your circuit is over 100A, or when you are using THHN/THWN-2 in conduit and have verified that both the breaker lugs and the termination lugs at the appliance are explicitly stamped "75°C". The 90°C column is almost exclusively used as a starting point for derating calculations, not for final ampacity selection.

Derating: When the Chart Value Drops

The base values in the chart above assume perfect conditions: an ambient temperature of 30°C (86°F) and no more than three current-carrying conductors (CCCs) in a single conduit. When real-world conditions violate these assumptions, you must apply derating factors, which effectively reduce the wire's ampacity.

Ambient Temperature Derating: If you run wire through an attic in the summer where temperatures reach 50°C (122°F), you must multiply the base ampacity by a correction factor. For THHN (90°C rated wire), the 50°C ambient correction factor is 0.82. If you are using 10 AWG THHN (base 90°C ampacity = 40A), the derated ampacity becomes 32.8A. You then compare this derated value to your termination column (e.g., 30A at 60°C) and use the lower of the two.

Conduit Fill (Bundling) Derating: If you pull more than three CCCs in a single raceway, the wires heat each other up. For 4 to 6 CCCs, you must multiply the 90°C base ampacity by 80%. For 7 to 9 CCCs, multiply by 70%. Note that a ground wire does not count as a CCC, but a neutral wire carrying unbalanced current (like in a multi-wire branch circuit or standard 120V circuit) does count.

What This Table Cannot Tell You

Ampacity charts are strictly about thermal limits—preventing the wire insulation from melting. They do not account for electrical efficiency or physical installation constraints. As noted by experts at Mike Holt Enterprises, relying solely on ampacity tables leads to two major field failures:

  1. Voltage Drop: The NEC recommends a maximum 3% voltage drop for branch circuits. If you run a 12 AWG copper wire 120 feet to a 15A window AC unit, the wire won't overheat (it's within the 20A ampacity limit), but the voltage at the outlet will drop below 114V, causing the compressor to stall and burn out. For long runs, you must upsize the wire purely for voltage drop, regardless of the ampacity chart.
  2. Physical Lug Fit: You might calculate that 1/0 AWG aluminum is perfectly rated for a 100A subpanel feeder based on the 75°C column. However, many standard 100A main breaker lugs are physically too small to accept 1/0 AWG stranded wire. Always check the manufacturer's spec sheet for the breaker's maximum wire acceptance range before purchasing heavy-gauge feeders.

Decision Tree: Pick Your Exact Wire Size

Follow this path to terminate your sizing decision with a concrete pick. Do not skip steps.

StepConditionAction / Result
1Are you using NM-B (Romex) cable?YES: Go to Step 4 (Use 60°C column).
NO: Go to Step 2.
2Are you using THHN/THWN-2 in conduit?YES: Go to Step 3.
NO: Consult specialized cable tables (e.g., UF-B or USE-2).
3Is the circuit breaker or load rated over 100A?YES: Use the 75°C column for final sizing.
NO: Go to Step 4.
4Circuit is 100A or less, using NM-B or standard THHN.ACTION: Use the 60°C column for your final ampacity pick.
5Are there more than 3 current-carrying conductors in the conduit, or is ambient temp > 86°F?YES: Calculate derating using the 90°C column, then verify the result is still higher than your breaker size.
NO: Proceed to Step 6.
6Is the one-way wire run longer than 75 feet?YES: Calculate voltage drop. Upsize wire by one gauge if drop > 3%.
NO: Your pick is final.
The Final Default Recommendation: If you are wiring a standard residential branch circuit, your lugs are unmarked, and you want a guaranteed code-compliant baseline without doing complex derating math: Default to the Copper 60°C column. Buy 14 AWG for 15A, 12 AWG for 20A, 10 AWG for 30A, 8 AWG for 40A, and 6 AWG for 50A. When in doubt, moving up one AWG size costs slightly more in copper but entirely eliminates thermal and voltage drop anxieties.