Reference table

Wire gauge chart

Every AWG size from 4/0 down to 40 and every kcmil size up to 1000, with the diameter, circular mils, square millimeters and DC resistance all computed from the gauge definition instead of retyped — beside the three ampacity columns of NEC Table 310.16 and a cross-reference to the IEC 60228 metric sizes. It costs nothing, and it prints onto one sheet with the header, the ads and the prose stripped out. There is no form on this page: it says what a gauge number is, not which one to use.

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Which part of the series

Every figure below comes out of one line of arithmetic — d = 0.005 × 92^((36 − n)/39) — so the diameter, the circular mils, the square millimeters and the resistance all descend from the same definition instead of being retyped out of four different books.

Sizes shown

21 rows. Building wire is listed the way Table 310.16 prints it, 14 AWG at the top; the small-gauge slice is listed by gauge number, which is the same order seen from the other end.

Printing drops the header, the ads and the prose and leaves the three tables.

Gauge geometry and DC resistance

Diameter here is the metal and not the insulation, and for a stranded conductor it is the equivalent solid diameter. Resistance is for a solid conductor at 75 °C, the temperature NEC Chapter 9 Table 8 states its column at.

American Wire Gauge diameter, area and direct-current resistance by size
Size	Diameter (in)	Diameter (mm)	Area (cmil)	Area (mm²)	Cu Ω/1000 ft	Al Ω/1000 ft	Cu Ω/km
14 AWG	0.0641	1.628	4,107	2.08	3.07	5.06	10.08
12 AWG	0.0808	2.053	6,530	3.31	1.93	3.18	6.34
10 AWG	0.1019	2.588	10,383	5.26	1.21	2.00	3.99
8 AWG	0.1285	3.264	16,510	8.37	0.764	1.26	2.51
6 AWG	0.1620	4.115	26,251	13.3	0.480	0.791	1.58
4 AWG	0.2043	5.189	41,741	21.15	0.302	0.498	0.991
3 AWG	0.2294	5.827	52,635	26.67	0.240	0.395	0.786
2 AWG	0.2576	6.544	66,371	33.63	0.190	0.313	0.623
1 AWG	0.2893	7.348	83,693	42.41	0.151	0.248	0.494
1/0 AWG	0.3249	8.251	105,535	53.48	0.120	0.197	0.392
2/0 AWG	0.3648	9.266	133,077	67.43	0.0948	0.156	0.311
3/0 AWG	0.4096	10.405	167,806	85.03	0.0752	0.124	0.247
4/0 AWG	0.4600	11.684	211,600	107.22	0.0596	0.0982	0.196
250 kcmil	0.5000	12.7	250,000	126.68	0.0505	0.0831	0.166
300 kcmil	0.5477	13.912	300,000	152.01	0.0420	0.0692	0.138
350 kcmil	0.5916	15.027	350,000	177.35	0.0360	0.0593	0.118
400 kcmil	0.6325	16.064	400,000	202.68	0.0315	0.0519	0.103
500 kcmil	0.7071	17.961	500,000	253.35	0.0252	0.0415	0.0828
600 kcmil	0.7746	19.675	600,000	304.02	0.0210	0.0346	0.0690
750 kcmil	0.8660	21.997	750,000	380.03	0.0168	0.0277	0.0552
1000 kcmil	1.0000	25.4	1,000,000	506.71	0.0126	0.0208	0.0414

American Wire Gauge definition: d = 0.005 in × 92^((36 − n)/39), with 1/0 = n 0, 2/0 = −1, 3/0 = −2, 4/0 = −3. Circular mils are the square of the diameter in mils, by definition. kcmil sizes are named by area; their diameter is √(area) and is not a gauge number. Reproduces the diameters and areas of NEC Chapter 9, Table 8.

This is the diameter of the conductor metal — for a stranded conductor it is the equivalent solid diameter, not the overall diameter over the strands. Conduit fill and terminal work need the overall diameter, which is larger because of the gaps between strands, and is tabulated in NEC Chapter 9 Tables 5 and 8. NEC Table 8 rounds diameters to four decimals before squaring, so its circular-mil column differs from the values here in the last digit or two (2 AWG: 66,360 printed against 66,371 computed).

Ampacity, NEC Table 310.16

The one table on this page nobody generated: a committee chose these numbers and no formula yields them. They assume three current-carrying conductors at 30 °C ambient, in a raceway, in a cable or directly buried. Each one still has to survive an ambient correction, a conductor-count adjustment and the 110.14(C) termination limit before it becomes a legal answer.

Allowable ampacity by conductor size, metal and insulation temperature rating
Conductor size	Copper			Aluminum
Size	Cu 60 °C	Cu 75 °C	Cu 90 °C	Al 60 °C	Al 75 °C	Al 90 °C
14 AWG	15	20	25	—	—	—
12 AWG	20	25	30	15	20	25
10 AWG	30	35	40	25	30	35
8 AWG	40	50	55	35	40	45
6 AWG	55	65	75	40	50	55
4 AWG	70	85	95	55	65	75
3 AWG	85	100	115	65	75	85
2 AWG	95	115	130	75	90	100
1 AWG	110	130	145	85	100	115
1/0 AWG	125	150	170	100	120	135
2/0 AWG	145	175	195	115	135	150
3/0 AWG	165	200	225	130	155	175
4/0 AWG	195	230	260	150	180	205
250 kcmil	215	255	290	170	205	230
300 kcmil	240	285	320	195	230	260
350 kcmil	260	310	350	210	250	280
400 kcmil	280	335	380	225	270	305
500 kcmil	320	380	430	260	310	350
600 kcmil	350	420	475	285	340	385
750 kcmil	400	475	535	320	385	435
1000 kcmil	455	545	615	375	445	500

A dash is a cell the table does not publish, not a zero and not a figure to interpolate: aluminum starts at 12 AWG because nothing smaller is listed for it, and a size outside the rows above has no ampacity on this page at all.

NEC (NFPA 70) 2023, Table 310.16 — Ampacities of Insulated Conductors with Not More Than Three Current-Carrying Conductors in Raceway, Cable, or Earth (Directly Buried), Based on Ambient Temperature of 30 °C (86 °F). Numbered Table 310.15(B)(16) in the 2017 and earlier editions. Aluminum column covers copper-clad aluminum.

Sizes 700, 800 and 900 kcmil and 1250 through 2000 kcmil are in the code table and are omitted here, so a size search that passes 600 kcmil returns 750 and over-sizes rather than guessing. 18 and 16 AWG, which the 2020 edition added at 90 °C only, are likewise omitted. This table is for conductors in a raceway, cable, or directly buried; conductors in free air are Table 310.17, and 1-kV single conductors outdoors are 310.20 — different tables with much higher values. Three conditions have to be applied to any figure taken from here before it is a legal answer: the ambient correction of 310.15(B)(1), the conductor-count adjustment of 310.15(C)(1), and the termination temperature limit of 110.14(C).

Metric cross-reference

A drawing in square millimeters against a spool marked in gauge numbers. The two series were never meant to line up and they do not, so each metric size gets the nearest gauge on both sides of it rather than one gauge presented as an equivalent.

IEC 60228 nominal conductor areas against the nearest AWG size above and below each
IEC size	Largest AWG at or under	Its area (mm²)	Smallest AWG at or over	Its area (mm²)
1.5 mm²	16 AWG	1.31	15 AWG	1.65
2.5 mm²	14 AWG	2.08	13 AWG	2.62
4 mm²	12 AWG	3.31	11 AWG	4.17
6 mm²	10 AWG	5.26	9 AWG	6.63
10 mm²	8 AWG	8.37	7 AWG	10.55
16 mm²	6 AWG	13.3	5 AWG	16.77
25 mm²	4 AWG	21.15	3 AWG	26.67
35 mm²	2 AWG	33.63	1 AWG	42.41
50 mm²	1 AWG	42.41	1/0 AWG	53.48
70 mm²	2/0 AWG	67.43	3/0 AWG	85.03
95 mm²	3/0 AWG	85.03	4/0 AWG	107.22
120 mm²	4/0 AWG	107.22	250 kcmil	126.68
150 mm²	250 kcmil	126.68	300 kcmil	152.01
185 mm²	350 kcmil	177.35	400 kcmil	202.68
240 mm²	400 kcmil	202.68	500 kcmil	253.35
300 mm²	500 kcmil	253.35	600 kcmil	304.02
400 mm²	750 kcmil	380.03	1000 kcmil	506.71
500 mm²	750 kcmil	380.03	1000 kcmil	506.71
630 mm²	1000 kcmil	506.71	—	—

IEC 60228 (BS EN 60228), Conductors of insulated cables, Table 1 — nominal cross-sectional areas of Class 1 solid and Class 2 stranded conductors.

A nominal area is a name, not a measurement: IEC 60228 specifies each size by a maximum resistance per kilometer, and a Class 2 stranded conductor of a given nominal area is physically a little larger than the number suggests. The AWG figures beside it are geometric areas of the metal.

An em dash in the last two columns means the AWG series has run out rather than that the answer is small: 1000 kcmil is 506.7 mm², so nothing here reaches 630 mm² as a single conductor.

The numbers run backwards because the gauge counts drawing operations rather than size. Wire is pulled through successively smaller dies, and n is how many passes it took, so a bigger number is a thinner wire. The ratio between adjacent sizes is fixed at 92^(1/39) ≈ 1.1229 in diameter, which is where the three shop rules come from: six gauge steps double the diameter, three steps double the area, and ten steps multiply the area by ten. Worked once: 12 AWG is 0.005 × 92^((36 − 12)/39) = 0.0808 in, and the diameter in mils squared is 6,530 circular mils.

Past 4/0 the counting stops, because a rope of that size is no longer drawn through a die. Larger conductors are named by area instead: 250 kcmil means 250,000 circular mils, so a kcmil designation is a measurement while a gauge number is an index. The two series meet at 4/0, which is 211.6 kcmil, and that is also why 4/0 comes out at exactly 0.4600 in — the gauge definition is indexed so that it does.

Underneath, the code book stops before this table does. NEC Chapter 9 Table 8 ends at 18 AWG and Table 310.16 ends at 14 AWG. Sizes 19 through 40 in the first table are the gauge definition carried on downwards and have no code entry to check against, which is a fine thing to wind a coil with and is not an ampacity for a branch circuit.

How to read a size off this chart

Three tables: what the gauge measures, what the code lets it carry, and what it is called in the other measuring system.

Choose the slice you are working in
Building wire lists the 21 sizes NEC Table 310.16 covers, 14 AWG at the top the way the code book prints it. Small gauge runs 14 through 40 for control, signal and coil work. The full series shows all 52 rows, from 40 AWG up through 1000 kcmil.
Read across a row rather than down a column
One row is one conductor described five ways: inches and millimeters of metal, circular mils and square millimeters of area, and ohms per thousand feet and per kilometer. The diameter is the conductor itself — for a stranded conductor the equivalent solid diameter — so it is not the number to measure a spool against with calipers.
Print it and put it inside the panel door
The print button drops the site header, the advertisement slots, the breadcrumbs, the FAQ and the About prose, and leaves the three tables with headers that repeat on every page and rows that do not split across a break. Nothing is rendered on a server to do it.

Technical specifications

Gauge definition	d = 0.005 in × 92^((36 − n)/39), with 1/0 indexed at n = 0 and 4/0 at n = −3 — the indexing that makes 4/0 come out at exactly 0.4600 in and 211,600 circular mils
Rows generated	44 AWG sizes from 4/0 through 40 AWG, plus 8 sizes named by area from 250 to 1000 kcmil, sorted by area rather than by name
Ratio between adjacent sizes	92^(1/39) = 1.1229 in diameter and 1.2610 in area, which is where the shop rules come from: six steps double the diameter, three steps double the area, ten steps multiply the area by ten
Resistivity behind the ohms column	10.371 Ω·cmil/ft for 100% IACS annealed copper and 17.002 for 61.0% IACS aluminum, both at 20 °C and both corrected to the 75 °C at which NEC Chapter 9 Table 8 states its figures
Ampacity table	21 sizes × 3 insulation temperature ratings × 2 metals, transcribed from NEC Table 310.16 because a committee chose those numbers and no formula produces them
Metric cross-reference	19 IEC 60228 nominal areas from 1.5 to 630 mm², each with the largest AWG size at or under it and the smallest at or over it
Where the code book stops	NEC Chapter 9 Table 8 ends at 18 AWG and Table 310.16 ends at 14 AWG. Sizes 19 through 40 here are the gauge definition carried onwards, with no code entry to check them against and no ampacity attached
What is transmitted to display it	Nothing. The tables are computed in the tab from a formula and two resistivities, so the chart works with the connection off

Frequently asked questions

Why do the gauge numbers get bigger as the wire gets thinner?

Because the number counts drawing operations rather than size. Wire is made by pulling rod through a die, then through a smaller die, and so on, and the gauge number is how many passes it took — so 18 AWG has been through more dies than 12 AWG and is thinner for it. The scale was later fixed to a geometric series so the steps are consistent: 36 AWG is 0.005 in, 4/0 is 0.4600 in, and the 39 steps between them are the 39th root of the ratio, which is 92^(1/39) per step.

Is 4/0 the same thing as 0000, and what is 1/0?

Yes — 4/0 is written 0000 and read 'four aught', and the two notations mean the same size. The series runs 2 AWG, 1 AWG, then 1/0, 2/0, 3/0, 4/0, because the numbers had already reached 1 and the wire kept getting bigger. In the gauge formula 1/0 is n = 0, 2/0 is n = −1, 3/0 is n = −2 and 4/0 is n = −3, which is the indexing that puts 4/0 at its published 0.4600 in.

What is a circular mil, and why not just use square inches?

A circular mil is the area of a circle one mil — one thousandth of an inch — in diameter, so the area of any round conductor in circular mils is simply its diameter in mils squared, with no π in it. That is the whole point: conductors are round, and the unit removes a constant that would otherwise appear in every calculation. It also keeps the numbers in a readable range, since 4/0 is 211,600 circular mils and 0.166 square inches.

Which metric size replaces 12 AWG?

Nothing exactly, which is why the cross-reference gives two answers. 12 AWG is 3.31 mm² of metal, and the IEC 60228 series jumps from 2.5 to 4 mm² around it — so 2.5 mm² is smaller than 12 AWG and 4 mm² is larger. Substituting one for the other is a decision about ampacity and about what the terminations are listed for, not a units conversion, and neither of those is on this page.

Does the diameter column include the insulation?

No. Every diameter here is the conductor metal, and for a stranded conductor it is the equivalent solid diameter — the diameter a solid conductor of the same cross-sectional area would have. The overall diameter over the strands is larger because of the gaps between them, and the diameter over the insulation is larger again; both of those live in NEC Chapter 9 Table 5 and are what conduit fill and terminal work need.

Why does my code book differ from this chart in the last digit?

Two reasons, both harmless. NEC Chapter 9 Table 8 rounds each diameter to four decimals before squaring it, so its circular-mil column differs slightly from one computed at full precision — 2 AWG reads 66,360 printed against 66,371 computed. And Table 8's resistance columns are for stranded and for coated conductors, which run about 2% and about 4% above the solid uncoated figures shown here, because a strand laid helically is longer than the cable that contains it.

Can I just use the 90 °C ampacity column?

Only as a starting point, never as the final figure. NEC 110.14(C) holds the ampacity of a conductor to the lowest temperature rating of any termination, device or conductor connected to it, and most breakers and lugs are marked 75 °C. The 90 °C column earns its keep by giving you a larger number to apply the ambient and bundling corrections to, so a hot or crowded raceway eats into headroom instead of into the answer.

About the American Wire Gauge and the tables built on it

The gauge is one of the few things in this trade that is a closed-form definition rather than a committee table, and that is worth knowing because it means a chart of it cannot legitimately disagree with another chart. Every diameter, area and resistance on this page descends from d = 0.005 in × 92^((36 − n)/39) and two published resistivities, so there is no transcription step in which a digit can go missing. Charts that were typed rather than generated do contain such errors, and the way to spot one is the ratio test: adjacent sizes must differ by 1.1229 in diameter and 1.2610 in area everywhere in the series, with no exceptions and no rounding drift.

The ampacity table on this page is the opposite kind of object and deserves to be read differently. Nobody derives 20 A for 12 AWG copper at 75 °C; it is a value a code-making panel settled on, based on how hot a conductor gets in an assumed installation, and it comes with three conditions attached before it is legal to use. That is also why a bare ampacity figure is not a wire size: correcting it for ambient, adjusting it for bundling and capping it at the termination rating is what the wire size calculator does, and checking that the conductor still delivers usable voltage at the far end is what the voltage drop calculator does. If you arrived here to look up a current rather than a size, the amperage calculator converts a load into amperes first, and the electrical calculator is where the underlying relations live for when you want the algebra rather than a sizing decision.

The resistance columns are the ones people underuse. Ohms per thousand feet is what turns a gauge number into a real electrical quantity: it is the input to a voltage drop calculation, it tells you what a long thermocouple extension does to a reading, and it is how you check a suspect run with a meter instead of a guess. Note the temperature: these are stated at 75 °C, and a conductor sitting at room temperature has roughly 10% less resistance than the table says. Note also the ceiling — above about 1/0, and on any load below about 0.9 power factor, resistance stops being the whole story and inductive reactance matters. NEC Chapter 9 Table 9 tabulates both for steel and PVC raceway; this site does not reproduce it, and a page here that runs past that boundary says so rather than quietly extrapolating. The conductors also have to fit somewhere, which is the conduit fill calculator. Whatever this chart says, the edition of the NEC your jurisdiction has adopted is the one that governs, and a printed page taped inside a panel is a reference rather than an approval.

What this chart sends anywhere

Every number on this page is worked out by JavaScript running in the tab you are reading it in. Nothing you type — loads, lengths, nameplate ratings, the rates your utility charges you — is uploaded, logged or kept, which is also why the calculators carry on working in a mechanical room with no signal.

There is not much to send in the first place: this page has no input fields, and the only thing you choose is which rows to display. That choice is not remembered between visits either — reload the page and it is back on the building-wire slice.