Electrical

Insulated Conductor Area by Insulation Type

Approximate cross-sectional area of THHN, XHHW, TW, THW, and RHW conductors from 14 AWG to 1000 kcmil, the figures that are summed for conduit fill.

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Source of these values

Approximate diameters as commonly published for NFPA 70 Chapter 9 Table 5. Areas are computed as pi/4 times the diameter squared, which is how the table is derived, and every value is checked at build time against a separately recorded copy of the published area. Verify against your adopted edition and the manufacturer data for the specific product.

Size	THHN, THWN, THWN-2, sq in	XHHW, XHHW-2, XHH, sq in	TW, sq in	THW, THHW, THW-2, sq in	RHH, RHW, RHW-2 (with outer covering), sq in
14	0.0097	0.0139	0.0139	0.0209	0.0293
12	0.0133	0.0181	0.0181	0.0260	0.0353
10	0.0211	0.0243	0.0243	0.0333	0.0437
8	0.0366	0.0437	0.0437	0.0556	0.0835
6	0.0507	0.0590	0.0726	0.0726	0.1041
4	0.0824	0.0814	0.0973	0.0973	0.1333
3	0.0973	0.0962	0.1134	0.1134	0.1521
2	0.1158	0.1146	0.1333	0.1333	0.1750
1	0.1562	0.1534	0.1901	0.1901	0.2660
1/0	0.1855	0.1825	0.2223	0.2223	0.3039
2/0	0.2223	0.2190	0.2624	0.2624	0.3505
3/0	0.2679	0.2642	0.3117	0.3117	0.4072
4/0	0.3237	0.3197	0.3718	0.3718	0.4754
250 kcmil	0.3970	0.3904	0.4596	0.4596	0.6291
300 kcmil	0.4608	0.4536	0.5281	0.5281	0.7088
350 kcmil	0.5242	0.5166	0.5958	0.5958	0.7870
400 kcmil	0.5863	0.5782	0.6619	0.6619	0.8626
500 kcmil	0.7073	0.6984	0.7901	0.7901	1.0082
600 kcmil	0.8676	0.8709	0.9729	0.9729	1.2135
750 kcmil	1.0496	1.0532	1.1652	1.1652	1.4272
1000 kcmil	1.3478	1.3519	1.4784	1.4784	1.7719

In short

The space a conductor occupies in a raceway depends on its insulation, not just its gauge. A 12 AWG THHN conductor is about 0.0133 square inches, the same size in THW is 0.0260, and in RHW with its outer covering 0.0353, nearly three times the THHN figure. Using THHN areas for another insulation understates fill.

Notes and limits

TW and THW share dimensions from 6 AWG up; they differ only in 14 through 8 AWG.
RHH, RHW and RHW-2 are listed with their outer covering. Without it they are smaller, and the code table has a separate column for that case.
Compact-stranded conductors are smaller and use Chapter 9 Table 5A, which is not reproduced here.
These are approximate dimensions. The manufacturer data for a specific product governs where it differs.

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