For any standard 20A residential branch circuit, you need 12 AWG copper wire. For a 30A dryer circuit, you need 10 AWG copper. These baseline numbers come directly from NEC Table 310.16, the master reference for wire sizing in the United States. However, blindly pulling wire without understanding the temperature columns and derating factors is how DIYers end up with tripped breakers or melted terminations. This guide provides a complete, bookmark-friendly printable wire ampacity chart, explains exactly how to read the temperature columns, and gives you a concrete decision path to pick your wire and breaker without guessing.

How to Read the NEC 310.16 Ampacity Table

The ampacity table is divided into three temperature columns for both copper and aluminum: 60°C, 75°C, and 90°C. The most common mistake hobbyists and junior electricians make is sizing wire based on the 90°C column because it allows for smaller, cheaper wire. You cannot use the 90°C column for your final breaker sizing in most residential applications.

Here is the rule: Your circuit's ampacity is limited by the lowest temperature rating of any connected component, termination, or conductor. Modern circuit breakers and receptacles are typically rated for 75°C, while older devices or specific small-gauge circuits (14, 12, and 10 AWG under NEC 240.4(D)) are legally capped at their 60°C equivalents. The 90°C column is strictly used as your starting baseline for calculating derating factors (like bundling wires in a conduit or high ambient heat). Once you apply the derating math, you compare that result to the 75°C or 60°C column to find your final allowable ampacity.

The Master Printable Wire Ampacity Chart

The data below is sourced directly from NFPA 70 (National Electrical Code) Table 310.16. It assumes an ambient temperature of 30°C (86°F) and not more than three current-carrying conductors in a raceway. Use the quick-jump links below to skip to the most queried residential sizes.

Quick Jump: 14 AWG | 12 AWG | 10 AWG | 8 AWG | 6 AWG | 4 AWG | 2 AWG

AWG / kcmil 60°C Copper 75°C Copper 90°C Copper 60°C Aluminum 75°C Aluminum 90°C Aluminum
14152025———
12202530152025
10303540253035
8405055304045
6556575405055
4708595556575
385100115657585
2951151307590100
111013014585100115
1/0125150170100120135
2/0145175195115135150
3/0165200225130155175
4/0195230260150180205
Pro Tip: Notice that 14, 12, and 10 AWG aluminum are marked with a dash (—). The NEC prohibits the use of aluminum wire smaller than 8 AWG for branch circuits and feeders due to its higher thermal expansion rate and historical termination failures.

Derating Factors: When Base Ampacity Drops

The ampacities in the chart above assume ideal conditions: an ambient temperature of 30°C (86°F) and no more than three current-carrying conductors in a single conduit. When you deviate from these conditions, you must apply derating factors from NEC Table 310.15(C)(1) to the 90°C column, regardless of your termination temperature rating.

Worked Numeric Example: You are pulling four current-carrying conductors (two 240V circuits sharing a neutral is not applicable here, so we count all four hot wires) through a single conduit in a standard garage. You want to use 10 AWG THHN copper for a 30A circuit.

  1. Find the 90°C base ampacity for 10 AWG copper: 40A.
  2. Look up the derating factor for 4 to 6 current-carrying conductors: 80%.
  3. Multiply: 40A × 0.80 = 32A.
  4. Compare the derated value (32A) to the 75°C termination limit for 10 AWG (35A). The lower number governs, so your final adjusted ampacity is 32A.
  5. Since 32A is greater than your 30A breaker size, 10 AWG THHN is perfectly legal and safe for this run.

If you had added a fifth current-carrying conductor, the derating factor would drop to 70% (40A × 0.70 = 28A). Because 28A is less than the 30A breaker, you would be forced to upsize to 8 AWG wire.

Decision Tree: Picking Your Exact Wire and Breaker

Stop guessing and use this decision matrix to lock in your materials list. This assumes standard residential NM-B (Romex) or THHN in conduit, copper conductors, and modern 75°C rated breakers.

Target Load / Application Required Breaker Concrete Wire Pick (Copper) Governing NEC Rule
Standard 15A Lighting Circuit 15 Amp 14 AWG 240.4(D)(1)
Standard 20A Receptacle Circuit 20 Amp 12 AWG 240.4(D)(2)
Electric Dryer / RV 30A Outlet 30 Amp 10 AWG 240.4(D)(3)
EV Charger / Hot Tub (40A continuous) 50 Amp 6 AWG 210.20(A) (125% rule)
100A Subpanel Feeder 100 Amp 2 AWG Copper (or 1/0 Aluminum) 310.12 (Residential Feeder)
Continuous Load Rule: If a load runs for 3 hours or more (like an EV charger or baseboard heater), you must multiply the load by 125% before sizing the wire and breaker. A 32A continuous EV charger requires 32 × 1.25 = 40A capacity, mandating a 50A breaker and 6 AWG wire, not 8 AWG.

What This Chart Cannot Tell You

While NEC Table 310.16 is the ultimate authority on thermal limits, it does not account for voltage drop over long distances. If you are running a 120V circuit to a detached shed 150 feet away, 12 AWG wire will technically handle the 20A thermal load, but the voltage at the shed will drop below 114V under heavy load, causing motors to overheat and lights to dim. For runs exceeding 100 feet, use a voltage drop calculator and plan to upsize your wire by at least one AWG step (e.g., using 10 AWG for a 20A long-run circuit).

Furthermore, this chart assumes standard installation methods. If you are burying direct-burial UF-B cable in the earth, the ampacity is governed by different thermal dissipation rules (NEC Table 300.5), and if you are working in a commercial setting with high ambient temperatures (like an attic in Phoenix during summer), the ambient temperature correction factors will drastically reduce your baseline numbers. Always defer to the manufacturer's installation sheet for specific cable assemblies like THHN/THWN-2 and consult your local Authority Having Jurisdiction (AHJ) for regional amendments to the NEC.

The Default Recommendation: When in doubt on a standard residential branch circuit, default to the 60°C column for your final breaker sizing, use copper wire, and buy a reputable brand of THHN or NM-B. If your calculated derated ampacity falls between standard breaker sizes (like 32A), the NEC allows you to round up to the next standard breaker size (35A), but standardizing on 12 AWG for 20A and 10 AWG for 30A eliminates 95% of residential sizing errors.