When sizing conductors for a branch circuit or feeder, the physical dimensions of the wire dictate everything from conduit fill capacity to terminal lug compatibility. However, the American Wire Gauge (AWG) system is notoriously counterintuitive: a higher gauge number means a physically thinner wire. Furthermore, the printed AWG number only defines the cross-sectional area of the bare conducting metal, not the outer diameter of the insulated cable you actually pull through a wall.
Below is the definitive thickness actual size wire gauge chart for solid and stranded bare copper, mapped directly to the ampacity limits established in the National Electrical Code (NEC). Bookmark this page for quick bench and jobsite lookups.
How to Read This Wire Gauge Thickness Chart
Before pulling wire or terminating a lug, you need to understand how to apply the columns in the reference table below. The most common mistake DIYers and junior apprentices make is looking at the 90°C column because the wire insulation (like THHN) is rated for it, and then sizing the breaker to that higher number.
Which Column Applies to Your Installation?
For almost all residential and light commercial terminations (breakers, receptacles, switches), the equipment is rated for 75°C. However, NEC 110.14(C) and 240.4(D) mandate that for 14, 12, and 10 AWG copper wire, you must use the 60°C column for overcurrent protection, regardless of the insulation's higher temperature rating. Furthermore, if you are using NM-B (Romex) cable, NEC 334.80 restricts the entire cable assembly to the 60°C ampacity column, even if the individual THHN conductors inside are rated for 90°C.
How Derating Rows Modify the Base Value
The ampacities in the table assume an ambient temperature of 30°C (86°F) and no more than three current-carrying conductors bundled together. If you pull four or more current-carrying wires through a single conduit, or if the ambient temperature in an attic exceeds 86°F, you must apply derating factors from NEC Table 310.15(C)(1). The trick: You are allowed to use the 90°C column as your starting baseline for derating math, but the final derated ampacity cannot exceed the 60°C or 75°C limits of your terminations.
What This Table Cannot Tell You
This chart provides bare copper dimensions and thermal ampacity. It does not account for:
- Voltage Drop: For runs exceeding 50 feet, you must calculate voltage drop. A 12 AWG wire might be thermally safe for 20A, but will cause unacceptable voltage drop on a 100-foot run to a shed.
- Outer Diameter (OD):strong> The physical thickness of the insulated wire varies wildly. A 10 AWG THHN wire has a much smaller OD than a 10 AWG XHHW-2 or NM-B conductor. Always check the manufacturer's spec sheet for conduit fill calculations.
- Short-Circuit Withstand: Ampacity is for continuous thermal loading. Fault-current withstand requires separate engineering calculations.
Complete AWG Thickness and Actual Size Reference Table
The following data is sourced directly from NEC Chapter 9, Table 8 (conductor dimensions) and NEC Table 310.16 (ampacities for copper conductors).
| AWG Size | Bare Diameter (Inches) | Bare Diameter (mm) | Area (kcmil) | 60°C Ampacity | 75°C Ampacity | 90°C Ampacity |
|---|---|---|---|---|---|---|
| 14 | 0.0641 | 1.63 | 4.11 | 15A * | 20A | 25A |
| 12 | 0.0808 | 2.05 | 6.53 | 20A * | 25A | 30A |
| 10 | 0.1019 | 2.59 | 10.38 | 30A * | 35A | 40A |
| 8 | 0.1285 | 3.26 | 16.51 | 40A | 50A | 55A |
| 6 | 0.1620 | 4.11 | 26.24 | 55A | 65A | 75A |
| 4 | 0.2043 | 5.19 | 41.74 | 70A | 85A | 95A |
| 3 | 0.2294 | 5.83 | 52.62 | 85A | 100A | 110A |
| 2 | 0.2576 | 6.54 | 66.36 | 95A | 115A | 130A |
| 1 | 0.2893 | 7.35 | 83.69 | 110A | 130A | 145A |
| 1/0 | 0.3249 | 8.25 | 105.6 | 125A | 150A | 170A |
| 2/0 | 0.3648 | 9.27 | 133.1 | 145A | 175A | 195A |
| 3/0 | 0.4096 | 10.40 | 167.8 | 165A | 200A | 225A |
| 4/0 | 0.4600 | 11.68 | 211.6 | 195A | 230A | 260A |
* Note: Per NEC 240.4(D), overcurrent protection for 14, 12, and 10 AWG copper is strictly limited to 15A, 20A, and 30A respectively, regardless of the 75°C or 90°C column values.
Bookmark Quick-Jumps: Most Queried Residential Wire Sizes
Instead of scrolling through the full matrix, use these quick references for the most common residential branch circuits and appliance feeds.
- 14 AWG (0.0641" / 1.63mm): The absolute minimum for general lighting and receptacle circuits. Limited to 15A breakers. Increasingly, many jurisdictions and electricians skip 14 AWG entirely, standardizing on 12 AWG to prevent voltage drop and allow future circuit upgrades.
- 12 AWG (0.0808" / 2.05mm): The workhorse of modern residential wiring. Used for 20A kitchen small-appliance circuits, bathroom receptacles, and dedicated laundry circuits.
- 10 AWG (0.1019" / 2.59mm): Standard for 30A appliances like electric dryers (when using 10/3 NM-B) and heavy-duty window air conditioners.
- 8 AWG (0.1285" / 3.26mm): Frequently used for 40A circuits, such as older electric ranges or large HVAC condenser units. Note that 8 AWG solid wire is exceptionally stiff; stranded THHN is highly recommended for pulling into panels.
- 6 AWG (0.1620" / 4.11mm): The standard for 50A circuits, including modern electric ranges, subpanel feeders (up to 50A), and EV Level 2 chargers (when derated for continuous load).
- 4 AWG (0.2043" / 5.19mm): Commonly used for 60A subpanel feeders or large heat pump backup resistance strips.
- 2 AWG (0.2576" / 6.54mm): The go-to size for 100A subpanel feeders when using copper, though aluminum (1/0 AL) is often substituted for cost savings on feeder runs.
Frequently Asked Questions
Does the wire gauge thickness include the insulation?
No. The AWG system and the dimensions in the chart above refer strictly to the bare conducting metal. The outer diameter (OD) of the insulated wire depends entirely on the insulation type and thickness. For example, a 12 AWG wire with thin THHN insulation will easily fit into a conduit that might be completely jammed if you tried to pull 12 AWG wire with thick XHHW-2 or UF-B jacketing. Always consult the specific manufacturer's datasheet for outer diameter when calculating conduit fill.
Why is a higher AWG number physically thinner?
The AWG system is based on the historical manufacturing process of wire drawing. To make a wire thinner, the raw copper rod had to be pulled (drawn) through a series of progressively smaller dies. A wire that was drawn through 12 dies was designated 12 AWG; a wire drawn through 14 dies was drawn down further, making it physically thinner and assigning it the 14 AWG designation. Therefore, more draws equals a higher gauge number and a smaller physical thickness.
How do I measure actual wire size if the printing on the jacket is faded?
Never try to measure wire gauge by clamping a caliper over the plastic insulation jacket—insulation thickness varies too much to be accurate. Instead, use a wire stripper to remove about an inch of insulation, exposing the bare copper. Zero out your digital caliper and measure the bare copper diameter. Match your measurement to the 'Bare Diameter' columns in the chart above. If the wire is stranded, compress the strands tightly with the caliper jaws, but recognize that the reading will be slightly larger than the solid equivalent due to the air gaps between strands.
Can I use the 90°C column to size my home wiring breakers?
Almost never for the final breaker size. While THHN/THWN-2 wire in your walls is indeed rated for 90°C, the breakers, lugs, and receptacles you connect it to are typically only rated for 60°C or 75°C. The NEC requires the weakest link in the chain to dictate the maximum ampacity. The 90°C column is primarily a mathematical tool used as a starting point when you need to apply temperature or bundling derating factors, allowing you to preserve more ampacity before dropping down to the termination limits.
