THHN Wire Area Chart and Dimensions

For any conduit fill calculation, you need the cross-sectional area of each conductor in square inches. NEC Table 5 provides those areas for insulated conductors, and the values differ by insulation type because the thickness and material of the jacket change the overall diameter. A 12 AWG THHN has an area of 0.0092 in², while a 12 AWG XHHW is larger, 0.0139 in², because XHHW uses a thicker, heat-resistant cross-linked polyethylene jacket. Use this as a thhn wire area chart, but it also covers XHHW, THW, compact, and bare conductors so you can complete a fill check without flipping between three tables.

NEC 2023 Chapter 9 Table 5 lists dimensions for every approved insulation type, not just THHN. The diameter listed is the overall finished diameter of the conductor, including the jacket. A thicker insulation, such as the rubber-based RHW compared to the nylon-jacketed THHN, adds 0.01 to 0.05 inches per size, which compounds when you sum six or more conductors. For a 4 AWG conductor, THHN occupies 0.0471 in², but RHW occupies 0.0834 in², nearly 77% more area. Use the wrong insulation type in your fill calculation and you will either overload the raceway or undersize it and fail inspection.

THHN and its dual-rated variants THWN and THWN-2 share the same diameter and area in NEC Table 5 because the insulation construction is identical. The values below cover 14 AWG through 4/0 AWG for copper and aluminum conductors. Use these areas whenever you work with standard THHN or any of the dual-rated types.

THHN, THWN, THWN-2 Diameter And Area

• 14 AWG: 0.094 in diameter, 0.0069 in² area
• 12 AWG: 0.108 in, 0.0092 in²
• 10 AWG: 0.126 in, 0.0125 in²
• 8 AWG: 0.171 in, 0.0230 in²
• 6 AWG: 0.203 in, 0.0324 in²
• 4 AWG: 0.245 in, 0.0471 in²
• 3 AWG: 0.273 in, 0.0585 in²
• 2 AWG: 0.304 in, 0.0726 in²
• 1 AWG: 0.358 in, 0.1006 in²
• 1/0 AWG: 0.400 in, 0.1257 in²
• 2/0 AWG: 0.448 in, 0.1576 in²
• 3/0 AWG: 0.502 in, 0.1979 in²
• 4/0 AWG: 0.562 in, 0.2481 in²

A common mistake is using these THHN areas for XHHW conductors. For a 4/0 pull, the difference is 0.2481 in² for THHN versus 0.278 in² for XHHW, enough to push a marginal fill calculation over the 40% limit.

XHHW and XHHW-2 use a cross-linked polyethylene insulation that is thicker than THHN. NEC Table 5 lists separate dimensions for these types. A 6 AWG XHHW has an area of 0.0367 in² compared to 0.0324 in² for THHN. The jump is larger at heavier sizes: for 4/0 AWG, XHHW occupies 0.278 in² against THHN's 0.2481 in². Check the insulation type printed on the conductor jacket before pulling your numbers from the table.

THW and RHW conductors, both rated for wet locations, use thicker insulation than THHN. In NEC Table 5, a 12 AWG THW has a diameter of 0.122 in and area of 0.0117 in², 27% more area than the 0.0092 in² of a 12 AWG THHN. RHW and RHW-2, which use a rubber-based insulation, are larger still: a 4 AWG RHW occupies 0.0834 in². The table also includes USE, USE-2, Z, ZW, ZW-2, TFE, FEP, FEPB, PFA, PFA-2, SA, SIS, TBS, TA, TFF, XF, XHH, and ZHF. For any of these types, look up NEC 2023 Chapter 9 Table 5 directly because the dimensions are not interchangeable with THHN.

Compact stranded conductors, listed in NEC 2023 Chapter 9 Table 5A, are manufactured with compressed stranding to reduce the overall diameter. They are available in 6 AWG through 4/0 AWG for THHN, THWN, THWN-2, XHHW, and XHHW-2 types. A 4/0 AWG compact THHN has an area of 0.2043 in², 18% smaller than the standard THHN area of 0.2481 in². That saving can allow one more conductor in a trade size. However, compact conductors are not a drop-in replacement for all applications: the compact dimensions apply only when the conductor is marked as compact on the packaging or the spec sheet. Use a standard conductor where the calculation assumed compact and the fill will exceed the legal limit.

Bare copper and aluminum conductors, used for equipment grounding conductors and neutrals, have their dimensions in NEC 2023 Chapter 9 Table 8. The table gives diameter, cross-sectional area, weight per 1000 ft, and DC resistance at 25°C and 75°C. For fill calculations, you need the cross-sectional area. A 10 AWG bare copper conductor has an area of 0.0081 in², smaller than a 10 AWG THHN at 0.0125 in². The bare conductor area is used directly in the sum for fill. Table 8 covers 18 AWG through 4/0 AWG. For 4/0 AWG bare copper, the area is 0.1662 in², compared to 0.2481 in² for an insulated THHN of the same size.

The conduit fill calculator uses NEC 2023 Chapter 9 Table 5 dimensions for THHN, THWN, THWN-2, XHHW, XHHW-2, THW, RHW, RHW-2, and the compact variants from Table 5A. It also includes bare conductor dimensions from Table 8. If you are using a less common insulation type, such as Z, ZW, TFE, FEP, FEPB, PFA, PFA-2, SA, SIS, TBS, TA, TFF, XF, XHH, or ZHF, look up the area in the printed NEC and enter it manually. The calculator does not support aluminum conductor dimensions from Table 5A or Table 8 at this time.

The most common failure in a conduit fill calculation is grabbing the area from the wrong NEC table. You have THHN in your hand but pull the XHHW column by mistake. You compute using Table 5 when the conductor is compact and Table 5A applies. You forget the bare ground counts from Table 8. The fix is straightforward: read the insulation type off the conductor jacket before you open the table. That one check, confirming the exact type, eliminates the majority of fill errors on the first pass.