How do I convert AWG to mm2?

Take the diameter from the gauge formula, d = 0.005 x 92^((36 - n)/39) inches, convert it to millimetres, and work out pi/4 times its square. 12 AWG is 3.309 mm2, 10 AWG is 5.261 mm2, 4 AWG is 21.15 mm2. The two systems aren't interchangeable: a metric size isn't something you can order in North America, and the reverse is true too.

What size is 12 AWG in mm2?

3.309 mm2, from a diameter of 2.053 mm. The nearest metric size is 4 mm2, which is about 21 per cent larger.

Why do AWG numbers get smaller as the wire gets bigger?

The gauge number counts how many times the wire was drawn through a smaller die, so more passes meant thinner wire and a higher number. The numbers run out below one pass, which is why the largest gauges are written 1/0 through 4/0.

What does kcmil mean?

Thousands of circular mils. A circular mil is the area of a circle one thousandth of an inch across. Sizes above 4/0 aren't part of the gauge series and are named by area instead, so 500 kcmil is 500,000 circular mils, or about 253 mm2.

How many mm2 is 4/0 AWG?

107.2 mm2, from a diameter of 11.68 mm. It's often compared with 120 mm2, which is about 12 per cent larger, but they're different sizes and not substitutes for each other.

What is the resistance of copper wire per 1000 feet?

Resistance per metre is the resistivity of the metal divided by the cross-sectional area, and 1000 feet is 304.8 metres. For solid copper at 20 degrees C, 12 AWG comes to about 1.588 ohms per 1000 feet and 10 AWG to about 0.999. Stranded conductors are about 2 per cent higher, and resistance goes up about 0.39 per cent per degree above 20 degrees C.

Wire sizing step by step, on one circuit →

Wire gauge chart

AWG and kcmil sizes with diameter, area in mm², circular mils and resistance. Every figure on this page is calculated from the gauge formula, not copied from a table.

Fishtape: wire gauge

Size

Material

Construction

Conductor °C

AREA

—

DIAMETER

—

CIRCULAR MILS

—

RESISTANCE

—

PER 1000 FT

—

NEAREST METRIC SIZE, FOR ORIENTATION ONLY

—

The calculation sheet

Where these numbers come from

AWG is a geometric series with two fixed points. 36 AWG is 0.005 inch across, and 0000 AWG, written 4/0, is 0.46 inch. Between them are 39 steps, each the same ratio apart:

d = 0.005 × 92^{(36 − n) / 39} inch

Here n is the gauge number, with n = 0, −1, −2, −3 for 1/0 to 4/0. The area is π/4 × d². A circular mil is the area of a circle one thousandth of an inch across, so the circular mils are the diameter in mils, squared.

That’s why the whole table below can be calculated, and none of it comes from anyone’s copyrighted table. Sizes above 4/0 aren’t part of the gauge series. They’re named by area in thousands of circular mils, which is what kcmil means.

Why bigger numbers mean thinner wire

The gauge number roughly counts how many times the wire was drawn through a smaller die. More passes, thinner wire: 24 AWG is thin, 2 AWG isn’t. The numbers run out below one pass, so the big sizes are written 1/0, 2/0, 3/0 and 4/0.

Two rules of thumb come from the ratio: every 3 gauge numbers doubles or halves the area, and every 10 changes it about tenfold.

AWG and mm² don’t mix

The nearest metric column is only a rough guide. 4 AWG is 21.15 mm². That’s close to 25 mm² but not the same, and you can’t order 25 mm² from a North American supplier anyway. Swapping one for the other without noticing is how errors get into a design, so this site keeps the two apart. The nearest size in the other system is shown only as a note, with the difference in per cent.

The resistance columns

The resistance in the table is for a solid conductor at 20 °C, worked out as ρ/A from the resistivity of the metal: 1.7241 × 10⁻⁸ Ω·m for annealed copper at 100 % IACS, 2.8264 × 10⁻⁸ for aluminium at 61 %. In practice two things change it, and the calculator above handles both:

Stranding. The strands spiral, so they’re longer than the cable. The usual allowance is about 2 %, so the calculator uses 1.02 by default.
Temperature. Copper resistance goes up about 0.39 % per degree. At 75 °C it’s about 22 % higher than at 20 °C, which is why a voltage drop worked out at room temperature comes out too low.

If you need the drop along a run, use the voltage drop calculator.

AWG and kcmil

Diameter, area, circular mils and the resistance of a solid conductor at 20 °C, calculated from the formula above.

Size	Diameter mm	Diameter in	Area mm²	Circular mils	Copper Ω/km	Copper Ω/1000 ft	Aluminium Ω/km	Nearest metric
36 AWG	0.127	0.005	0.01267	25	1361	414.8	2231	0.5 mm² -97%
35 AWG	0.1426	0.005615	0.01597	32	1079	329	1769	0.5 mm² -97%
34 AWG	0.1601	0.006305	0.02014	40	856	260.9	1403	0.5 mm² -96%
33 AWG	0.1798	0.00708	0.0254	50	678.8	206.9	1113	0.5 mm² -95%
32 AWG	0.2019	0.00795	0.03203	63	538.3	164.1	882.5	0.5 mm² -94%
31 AWG	0.2268	0.008928	0.04039	80	426.9	130.1	699.8	0.5 mm² -92%
30 AWG	0.2546	0.01003	0.05093	101	338.5	103.2	555	0.5 mm² -90%
29 AWG	0.2859	0.01126	0.06422	127	268.5	81.83	440.1	0.5 mm² -87%
28 AWG	0.3211	0.01264	0.08098	160	212.9	64.9	349	0.5 mm² -84%
27 AWG	0.3606	0.0142	0.1021	202	168.9	51.47	276.8	0.5 mm² -80%
26 AWG	0.4049	0.01594	0.1288	254	133.9	40.81	219.5	0.5 mm² -74%
25 AWG	0.4547	0.0179	0.1624	320	106.2	32.37	174.1	0.5 mm² -68%
24 AWG	0.5106	0.0201	0.2047	404	84.21	25.67	138.1	0.5 mm² -59%
23 AWG	0.5733	0.02257	0.2582	509	66.78	20.36	109.5	0.5 mm² -48%
22 AWG	0.6438	0.02535	0.3255	642	52.96	16.14	86.82	0.5 mm² -35%
21 AWG	0.7229	0.02846	0.4105	810	42	12.8	68.85	0.5 mm² -18%
20 AWG	0.8118	0.03196	0.5176	1,022	33.31	10.15	54.6	0.5 mm² +4%
19 AWG	0.9116	0.03589	0.6527	1,288	26.41	8.051	43.3	0.75 mm² -13%
18 AWG	1.024	0.0403	0.823	1,624	20.95	6.385	34.34	0.75 mm² +10%
17 AWG	1.15	0.04526	1.038	2,048	16.61	5.063	27.23	1 mm² +4%
16 AWG	1.291	0.05082	1.309	2,583	13.17	4.015	21.6	1.5 mm² -13%
15 AWG	1.45	0.05707	1.65	3,257	10.45	3.184	17.13	1.5 mm² +10%
14 AWG	1.628	0.06408	2.081	4,107	8.285	2.525	13.58	2.5 mm² -17%
13 AWG	1.828	0.07196	2.624	5,178	6.571	2.003	10.77	2.5 mm² +5%
12 AWG	2.053	0.08081	3.309	6,530	5.211	1.588	8.542	4 mm² -17%
11 AWG	2.305	0.09074	4.172	8,234	4.132	1.26	6.774	4 mm² +4%
10 AWG	2.588	0.1019	5.261	10,383	3.277	0.9988	5.372	6 mm² -12%
9 AWG	2.906	0.1144	6.634	13,093	2.599	0.7921	4.26	6 mm² +11%
8 AWG	3.264	0.1285	8.366	16,510	2.061	0.6282	3.379	10 mm² -16%
7 AWG	3.665	0.1443	10.55	20,818	1.634	0.4982	2.679	10 mm² +5%
6 AWG	4.115	0.162	13.3	26,251	1.296	0.3951	2.125	16 mm² -17%
5 AWG	4.621	0.1819	16.77	33,102	1.028	0.3133	1.685	16 mm² +5%
4 AWG	5.189	0.2043	21.15	41,741	0.8152	0.2485	1.336	25 mm² -15%
3 AWG	5.827	0.2294	26.67	52,635	0.6464	0.197	1.06	25 mm² +7%
2 AWG	6.544	0.2576	33.63	66,371	0.5127	0.1563	0.8404	35 mm² -4%
1 AWG	7.348	0.2893	42.41	83,693	0.4066	0.1239	0.6665	35 mm² +21%
1/0 AWG	8.251	0.3249	53.48	105,535	0.3224	0.09827	0.5285	50 mm² +7%
2/0 AWG	9.266	0.3648	67.43	133,077	0.2557	0.07793	0.4192	70 mm² -4%
3/0 AWG	10.4	0.4096	85.03	167,806	0.2028	0.0618	0.3324	95 mm² -10%
4/0 AWG	11.68	0.46	107.2	211,600	0.1608	0.04901	0.2636	95 mm² +13%
250 kcmil	12.7	0.5	126.7	250,000	0.1361	0.04148	0.2231	120 mm² +6%
300 kcmil	13.91	0.5477	152	300,000	0.1134	0.03457	0.1859	150 mm² +1%
350 kcmil	15.03	0.5916	177.3	350,000	0.09722	0.02963	0.1594	185 mm² -4%
400 kcmil	16.06	0.6325	202.7	400,000	0.08506	0.02593	0.1394	185 mm² +10%
500 kcmil	17.96	0.7071	253.4	500,000	0.06805	0.02074	0.1116	240 mm² +6%
600 kcmil	19.67	0.7746	304	600,000	0.05671	0.01728	0.09297	300 mm² +1%
700 kcmil	21.25	0.8367	354.7	700,000	0.04861	0.01482	0.07969	400 mm² -11%
750 kcmil	22	0.866	380	750,000	0.04537	0.01383	0.07437	400 mm² -5%
800 kcmil	22.72	0.8944	405.4	800,000	0.04253	0.01296	0.06972	400 mm² +1%
900 kcmil	24.1	0.9487	456	900,000	0.03781	0.01152	0.06198	500 mm² -9%
1000 kcmil	25.4	1	506.7	1,000,000	0.03403	0.01037	0.05578	500 mm² +1%
1250 kcmil	28.4	1.118	633.4	1,250,000	0.02722	0.008297	0.04462	630 mm² +1%
1500 kcmil	31.11	1.225	760.1	1,500,000	0.02268	0.006914	0.03719	800 mm² -5%
1750 kcmil	33.6	1.323	886.7	1,750,000	0.01944	0.005926	0.03187	800 mm² +11%
2000 kcmil	35.92	1.414	1013	2,000,000	0.01701	0.005185	0.02789	1000 mm² +1%

Resistance is for a solid conductor at 20 °C, from ρ/A. Stranded conductors are about 2 % higher, and copper gains about 0.39 % per degree. The last column is a rough guide only: the two systems aren’t interchangeable.

Metric conductor sizes

The IEC 60228 sizes used outside North America, with the same columns. Metric sizes are defined by area, so the diameter shown is for a solid round conductor of that area.

Size	Diameter mm	Diameter in	Area mm²	Circular mils	Copper Ω/km	Copper Ω/1000 ft	Aluminium Ω/km	Nearest AWG or kcmil
0.5 mm2	0.7979	0.03141	0.5	987	34.48	10.51	56.53	20 AWG -3%
0.75 mm2	0.9772	0.03847	0.75	1,480	22.99	7.007	37.69	18 AWG -9%
1 mm2	1.128	0.04442	1	1,974	17.24	5.255	28.26	17 AWG -4%
1.5 mm2	1.382	0.05441	1.5	2,960	11.49	3.503	18.84	15 AWG -9%
2.5 mm2	1.784	0.07024	2.5	4,934	6.896	2.102	11.31	13 AWG -5%
4 mm2	2.257	0.08885	4	7,894	4.31	1.314	7.066	11 AWG -4%
6 mm2	2.764	0.1088	6	11,841	2.873	0.8758	4.711	9 AWG -10%
10 mm2	3.568	0.1405	10	19,735	1.724	0.5255	2.826	7 AWG -5%
16 mm2	4.514	0.1777	16	31,576	1.078	0.3284	1.766	5 AWG -5%
25 mm2	5.642	0.2221	25	49,338	0.6896	0.2102	1.131	3 AWG -6%
35 mm2	6.676	0.2628	35	69,073	0.4926	0.1501	0.8075	2 AWG +4%
50 mm2	7.979	0.3141	50	98,676	0.3448	0.1051	0.5653	1/0 AWG -6%
70 mm2	9.441	0.3717	70	138,147	0.2463	0.07507	0.4038	2/0 AWG +4%
95 mm2	11	0.433	95	187,485	0.1815	0.05532	0.2975	3/0 AWG +12%
120 mm2	12.36	0.4866	120	236,823	0.1437	0.04379	0.2355	250 kcmil -5%
150 mm2	13.82	0.5441	150	296,029	0.1149	0.03503	0.1884	300 kcmil -1%
185 mm2	15.35	0.6042	185	365,102	0.09319	0.02841	0.1528	350 kcmil +4%
240 mm2	17.48	0.6882	240	473,646	0.07184	0.0219	0.1178	500 kcmil -5%
300 mm2	19.54	0.7695	300	592,058	0.05747	0.01752	0.09421	600 kcmil -1%
400 mm2	22.57	0.8885	400	789,410	0.0431	0.01314	0.07066	800 kcmil -1%
500 mm2	25.23	0.9934	500	986,763	0.03448	0.01051	0.05653	1000 kcmil -1%
630 mm2	28.32	1.115	630	1,243,321	0.02737	0.008341	0.04486	1250 kcmil -1%
800 mm2	31.92	1.257	800	1,578,820	0.02155	0.006569	0.03533	1500 kcmil +5%
1000 mm2	35.68	1.405	1000	1,973,525	0.01724	0.005255	0.02826	2000 kcmil -1%

What a size chart can’t tell you

How much current a wire can carry. That depends on the insulation, the ambient temperature, how many loaded conductors are bundled together, how it’s installed, and the rules where you work. Those figures are in national wiring rules, which are copyrighted, so they aren’t here.

The app works through all of it at once and tells you which check decided the size. See the app.

More free calculators

Voltage drop calculator →

Single phase, three phase and DC, in mm², AWG or kcmil. Shows every step and gives you a sheet to print.

Wire size by voltage drop →

The smallest size that keeps the drop under your limit, plus a list of what it doesn’t check.

Ohm’s law and power →

Volts, amps or ohms from the other two, plus real power for single and three phase.

Conduit fill →

How full your conduit is, for any conduit and any cable, in mm or inches, against the limit from your rules.

The app

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