AWG Diameter Chart: Wire Size, Ampacity, and Physical Dimensions

When you strip back the jacket of a non-metallic cable or pull THHN through conduit, the physical thickness of the copper dictates both how much current it can safely carry and how much space it occupies. For the most common residential branch circuits, the baseline physical dimensions are: 14 AWG is 0.0641 inches (1.628 mm), 12 AWG is 0.0808 inches (2.053 mm), and 10 AWG is 0.1019 inches (2.588 mm).

The American Wire Gauge (AWG) system is logarithmic, meaning every 3-gauge decrease (e.g., from 12 AWG to 9 AWG) exactly doubles the cross-sectional area of the wire. This AWG diameter chart provides the exact physical dimensions, cross-sectional area, and National Electrical Code (NEC) ampacity ratings you need to size your next circuit correctly.

How to Read the AWG Diameter and Ampacity Table

Before pulling wire, you must understand which columns apply to your specific installation. The physical dimensions (diameter and area) in this chart are based on ASTM B258, the standard specification for solid round copper wires. The ampacity columns are derived from NEC Table 310.16, assuming copper conductors, an ambient temperature of 30°C (86°F), and no more than three current-carrying conductors bundled in a raceway.

Complete AWG Diameter Chart (Copper, 60°C & 75°C)

The following table covers the full range of standard building wire sizes. Ampacities listed are the base values before any environmental derating is applied.

* 18 and 16 AWG are not permitted for standard branch circuit wiring in residential NEC applications.
** Per NEC 240.4(D), small conductors (14, 12, and 10 AWG) are strictly limited to 15A, 20A, and 30A overcurrent protection respectively, regardless of the 75°C or 90°C insulation rating.

Bookmark Quick-Jump: The Most Queried Wire Sizes

For 90% of home wiring projects, you will only reach for five sizes. Here is the quick-reference data for the most common DIY and professional pulls:

• 14 AWG (15A max): 0.0641" diameter. Used for general lighting and standard bedroom/living room receptacles. Always protected by a 15A breaker.
• 12 AWG (20A max): 0.0808" diameter. The workhorse for kitchen, bathroom, and garage receptacle circuits. Required anywhere a 20A breaker is installed.
• 10 AWG (30A max): 0.1019" diameter. Standard for electric water heaters, window AC units, and standard electric dryers (when paired with a 10-3 cable).
• 8 AWG (40A/50A): 0.1285" diameter. Used for 40A circuits or 50A circuits when using THHN in conduit (NM-B 8 AWG is limited to 40A at 60°C).
• 6 AWG (55A/65A): 0.1620" diameter. The standard feeder size for 50A hot tubs, heavy-duty welder outlets, and small 60A subpanels.

Derating Factors: How Installation Modifies Base Values

The ampacities in the chart above assume ideal conditions: 30°C ambient air and no more than three current-carrying conductors in a single conduit. Real-world jobsites rarely offer ideal conditions. When you bundle wires or run them through hot attics, you must apply derating factors per NEC 310.15.

Worked Example: You are pulling four current-carrying 12 AWG THHN wires through a conduit in a standard indoor environment.
1. Base 90°C ampacity for 12 AWG is 30A.
2. NEC Table 310.15(C)(1) dictates an 80% adjustment factor for 4-6 bundled conductors.
3. 30A × 0.80 = 24A.
4. Because 24A exceeds the 20A termination limit for 12 AWG, you can safely protect this circuit with a standard 20A breaker. If you had six conductors (requiring a 50% derating to 15A), you would be forced to upsize to 10 AWG wire.

Wire Sizing Decision Path: Pick Your Exact AWG

Stop guessing and follow this decision tree to select your exact wire gauge and insulation type for standard residential copper installations.

What This Chart Cannot Tell You (And Where to Look Next)

An AWG diameter chart gives you physical thickness and thermal limits, but it omits three critical engineering constraints that can fail an inspection or cause equipment damage:

1. Voltage Drop Over Distance: This chart assumes short runs. If you are running a 12 AWG circuit 150 feet to a detached shed, the physical wire can handle 20A thermally, but the voltage drop will exceed the recommended 3% threshold, causing motors to overheat. For runs over 100 feet, you must calculate voltage drop and typically upsize the wire by one or two gauges.
2. Conduit Fill Capacity: Knowing the diameter of a single wire is not enough to know if it will fit in a pipe. NEC Chapter 9, Table 1 limits conduit fill to 40% for three or more wires. You must calculate the total cross-sectional area of all wires combined and compare it against the internal diameter of your specific PVC, EMT, or rigid metal conduit.
3. Short-Circuit Withstand (AIC Rating): Wire gauge does not dictate fault current survival. If your main service panel has a 42,000 Amp available fault current, the breaker you install must have a matching 42k AIC rating. A 10 AWG wire protected by a standard 10k AIC breaker in a high-fault panel is a severe safety hazard, regardless of its ampacity.