How many circular mils is 12 AWG?

6,530 cmil (3.31 mm²). 14 AWG is 4,110, 10 AWG 10,380, and every three gauge numbers roughly double the area.

What does kcmil mean?

Thousands of circular mils. Above 4/0 AWG (211,600 cmil) sizes are named by area: 250 kcmil is 250,000 circular mils. Older documents write MCM for the same unit.

Why do bigger wires have smaller gauge numbers?

The AWG number counts drawing steps through successively smaller dies, so a thinner wire has been drawn more times. Past 1 AWG the sequence continues as 1/0, 2/0, 3/0 and 4/0 (“one aught” to “four aught”) before switching to kcmil.

What is the resistance of 12 AWG copper per 1000 feet?

1.98 Ω per 1000 ft stranded, 1.93 Ω solid, both at 75 °C as Table 8 prints them. Table 8 Note 2 converts to another temperature: at 20 °C the stranded figure is about 1.63 Ω.

How do AWG sizes compare with mm² cable?

The mm² column is the metric area of the AWG size, not a metric cable size: 12 AWG is 3.31 mm², between 2.5 and 4 mm² IEC cable; 10 AWG is 5.261 mm², between 4 and 6 mm².

Is the diameter in this chart the size of the insulated wire?

No. Table 8 gives the bare conductor’s overall diameter. Insulated dimensions, which conduit fill depends on, are in Chapter 9 Table 5 and are used by the conduit fill chart.

Wire gauge chart: AWG and kcmil conductor properties

Area, stranding, diameter and DC resistance for every conductor size from 18 AWG to 2000 kcmil, as NEC Chapter 9 Table 8 prints them, with the 75 °C copper and aluminum ampacity from Table 310.16 alongside. These are the resistances the voltage drop calculator and the K-factors (12.9 copper, 21.2 aluminum) come from.

Chapter 9 Table 8: stranded conductors

Class B concentric stranding. Resistance is DC at 75 °C (167 °F), ohms per 1000 ft. Diameter is the overall bare conductor.

Size	Circular mils	mm²	Strands	Dia. in.	Dia. mm	Ω/kft Cu	Ω/kft Cu coated	Ω/kft Al	A Cu 75 °C	A Al 75 °C
18 AWG	1,620	0.823	7	0.046	1.16	7.95	8.45	13.10	—	—
16 AWG	2,580	1.31	7	0.058	1.46	4.99	5.29	8.21	—	—
14 AWG	4,110	2.08	7	0.073	1.85	3.14	3.26	5.17	20	—
12 AWG	6,530	3.31	7	0.092	2.32	1.98	2.05	3.25	25	20
10 AWG	10,380	5.261	7	0.116	2.95	1.24	1.29	2.04	35	30
8 AWG	16,510	8.367	7	0.146	3.71	0.778	0.809	1.28	50	40
6 AWG	26,240	13.3	7	0.184	4.67	0.491	0.510	0.808	65	50
4 AWG	41,740	21.15	7	0.232	5.89	0.308	0.321	0.508	85	65
3 AWG	52,620	26.67	7	0.260	6.6	0.245	0.254	0.403	100	75
2 AWG	66,360	33.62	7	0.292	7.42	0.194	0.201	0.319	115	90
1 AWG	83,690	42.41	19	0.332	8.43	0.154	0.160	0.253	130	100
1/0 AWG	105,600	53.49	19	0.372	9.45	0.122	0.127	0.201	150	120
2/0 AWG	133,100	67.43	19	0.418	10.62	0.0967	0.101	0.159	175	135
3/0 AWG	167,800	85.01	19	0.470	11.94	0.0766	0.0797	0.126	200	155
4/0 AWG	211,600	107.2	19	0.528	13.41	0.0608	0.0626	0.100	230	180
250 kcmil	250,000	127	37	0.575	14.61	0.0515	0.0535	0.0847	255	205
300 kcmil	300,000	152	37	0.630	16	0.0429	0.0446	0.0707	285	230
350 kcmil	350,000	177	37	0.681	17.3	0.0367	0.0382	0.0605	310	250
400 kcmil	400,000	203	37	0.728	18.49	0.0321	0.0331	0.0529	335	270
500 kcmil	500,000	253	37	0.813	20.65	0.0258	0.0265	0.0424	380	310
600 kcmil	600,000	304	61	0.893	22.68	0.0214	0.0223	0.0353	420	340
700 kcmil	700,000	355	61	0.964	24.49	0.0184	0.0189	0.0303	460	375
750 kcmil	750,000	380	61	0.998	25.35	0.0171	0.0176	0.0282	475	385
800 kcmil	800,000	405	61	1.030	26.16	0.0161	0.0166	0.0265	490	395
900 kcmil	900,000	456	61	1.094	27.79	0.0143	0.0147	0.0235	520	425
1000 kcmil	1,000,000	507	61	1.152	29.26	0.0129	0.0132	0.0212	545	445
1250 kcmil	1,250,000	633	91	1.289	32.74	0.0103	0.0106	0.0169	590	485
1500 kcmil	1,500,000	760	91	1.412	35.86	0.00858	0.00883	0.0141	625	520
1750 kcmil	1,750,000	887	127	1.526	38.76	0.00735	0.00756	0.0121	650	545
2000 kcmil	2,000,000	1013	127	1.632	41.45	0.00643	0.00662	0.0106	665	560

Source: NEC 2017 (NFPA 70-2017), Chapter 9 Table 8; identical in 2005/2014. 2017 text, 2014 cross-check. Ampacity columns: Table 310.16, 75 °C, three or fewer current-carrying conductors at 30 °C, before the 240.4(D) limits on 14 to 10 AWG.

Chapter 9 Table 8: solid conductors

Table 8 lists solid conductors from 18 to 8 AWG; area is the same as the stranded size, diameter and resistance are a little smaller.

Size	Dia. in.	Dia. mm	Ω/kft Cu	Ω/kft Cu coated	Ω/kft Al
8 AWG	0.128	3.264	0.764	0.786	1.26
10 AWG	0.102	2.588	1.21	1.26	2.00
12 AWG	0.081	2.05	1.93	2.01	3.18
14 AWG	0.064	1.63	3.07	3.19	5.06
16 AWG	0.051	1.29	4.89	5.08	8.05
18 AWG	0.040	1.02	7.77	8.08	12.80

Using the resistance column

The voltage dropped in a run is current × resistance of the whole loop. For 20 A on 12 AWG copper with 50 ft between panel and load, the loop is 100 ft: 20 × 1.98 × 100 ÷ 1000 = 3.96 V, 3.3 % of 120 V. Open this run; the calculator also gives the AC answer from Table 9.

Table 8 Note 2 adjusts resistance to another temperature: R₂ = R₁ × [1 + α (T₂ − 75)], with α = 0.00323 for copper and 0.0033 for aluminum.

Questions people ask

How many circular mils is 12 AWG?: 6,530 cmil (3.31 mm²). 14 AWG is 4,110, 10 AWG 10,380, and every three gauge numbers roughly double the area.
What does kcmil mean?: Thousands of circular mils. Above 4/0 AWG (211,600 cmil) sizes are named by area: 250 kcmil is 250,000 circular mils. Older documents write MCM for the same unit.
Why do bigger wires have smaller gauge numbers?: The AWG number counts drawing steps through successively smaller dies, so a thinner wire has been drawn more times. Past 1 AWG the sequence continues as 1/0, 2/0, 3/0 and 4/0 (“one aught” to “four aught”) before switching to kcmil.
What is the resistance of 12 AWG copper per 1000 feet?: 1.98 Ω per 1000 ft stranded, 1.93 Ω solid, both at 75 °C as Table 8 prints them. Table 8 Note 2 converts to another temperature: at 20 °C the stranded figure is about 1.63 Ω.
How do AWG sizes compare with mm² cable?: The mm² column is the metric area of the AWG size, not a metric cable size: 12 AWG is 3.31 mm², between 2.5 and 4 mm² IEC cable; 10 AWG is 5.261 mm², between 4 and 6 mm².
Is the diameter in this chart the size of the insulated wire?: No. Table 8 gives the bare conductor’s overall diameter. Insulated dimensions, which conduit fill depends on, are in Chapter 9 Table 5 and are used by the conduit fill chart.