Wire gauge chart: complete AWG ampacity, diameter, and resistance reference

Pick the wrong wire gauge and you face one of two failure modes: undersized wire overheats under load and becomes a fire hazard, or oversized wire wastes money on copper you don't need. The American Wire Gauge (AWG) system assigns a single number to every standard conductor size, but that number runs backward — the larger the AWG number, the smaller the wire. That counterintuitive scale trips up engineers and electricians alike, especially when crossing between AWG and metric wire sizes.

This reference covers the complete AWG range from 0000 (4/0) through 40 gauge, with physical dimensions in both inches and millimeters, DC resistance at 20 °C in ohms per 1000 ft, and ampacity ratings under NEC 310 for both copper and aluminum conductors. You'll also find a worked example sizing wire for a real circuit, a breakdown of how temperature correction affects ampacity, and answers to the questions that come up most often when reading these tables.

The underlying math comes from a precise geometric series. Each step up in AWG number reduces the conductor's cross-sectional area by a fixed ratio, which is why resistance increases predictably as gauge number rises. Understanding that relationship lets you extrapolate beyond any table, spot errors in vendor spec sheets, and make defensible design decisions rather than guesses.

How the AWG numbering system works

AWG was standardized in the United States in the mid-1800s and is defined by a geometric progression. The diameter of a 36 AWG wire is exactly 0.005 in (5 mils), and the diameter of a 0000 AWG wire is exactly 0.46 in (460 mils). Between those two endpoints, 38 intermediate sizes are spaced so that every 6 gauge steps multiplies the cross-sectional area by exactly 2 and every 3 gauge steps multiplies it by √2 ≈ 1.414.

The multiplier per single AWG step in diameter is the 39th root of 92, approximately 1.1229. So to find the diameter of any gauge, you divide the diameter of the next smaller AWG number by 1.1229. Resistance varies inversely with cross-sectional area, meaning each gauge step increases resistance by a factor of 1.1229² ≈ 1.261. Six gauge steps doubles the resistance; six gauge steps in the other direction halves it.

Sizes larger than 0 AWG use a different notation: 00, 000, and 0000 — written as 2/0, 3/0, and 4/0 respectively. Above 4/0 AWG, conductors are specified in kcmil (thousands of circular mils) rather than AWG. The 250 kcmil, 350 kcmil, and 500 kcmil conductors you see in commercial electrical work fall in this kcmil range.

Complete AWG wire gauge chart

The table below lists physical dimensions and DC resistance for solid copper conductors at 20 °C. Resistance values assume 100% IACS (International Annealed Copper Standard) conductivity. Real drawn wire runs 97–99% IACS, so actual resistance will be 1–3% higher than the values shown.

AWG	Diameter (in)	Diameter (mm)	Area (mm²)	Resistance (Ω/1000 ft)	Weight (lb/1000 ft)
0000 (4/0)	0.4600	11.684	107.2	0.049	641
000 (3/0)	0.4096	10.405	85.01	0.0618	508
00 (2/0)	0.3648	9.266	67.43	0.0779	403
0 (1/0)	0.3249	8.252	53.48	0.0983	320
1	0.2893	7.348	42.41	0.1239	253
2	0.2576	6.543	33.63	0.1563	201
3	0.2294	5.827	26.67	0.197	159
4	0.2043	5.189	21.15	0.2485	126
6	0.1620	4.115	13.30	0.3951	79.5
8	0.1285	3.264	8.367	0.6282	50.0
10	0.1019	2.588	5.261	0.9989	31.4
12	0.0808	2.053	3.309	1.588	19.8
14	0.0641	1.628	2.081	2.525	12.4
16	0.0508	1.291	1.309	4.016	7.82
18	0.0403	1.024	0.8231	6.385	4.92
20	0.0320	0.8128	0.5189	10.15	3.10
22	0.0253	0.6438	0.3255	16.14	1.94
24	0.0201	0.5106	0.2047	25.67	1.22
26	0.0159	0.4039	0.1281	40.81	0.765
28	0.0126	0.3211	0.0810	64.90	0.481
30	0.0100	0.2546	0.0509	103.2	0.303
32	0.00795	0.2019	0.0320	164.1	0.190
34	0.00630	0.1601	0.0201	260.9	0.120
36	0.00500	0.1270	0.0127	414.8	0.0757
38	0.00397	0.1007	0.00797	659.6	0.0476
40	0.00314	0.0799	0.00501	1049	0.0299

Use the  to find the minimum gauge for any load, voltage, and run length without manual table lookups.

NEC ampacity table: copper and aluminum conductors

Ampacity — the maximum continuous current a conductor can carry — depends on the insulation type, installation method, and ambient temperature. The NEC Table 310.16 values below apply to conductors in raceway, cable, or direct burial in an ambient temperature of 30 °C (86 °F). Three conditions determine which column to use: conductor material (copper vs aluminum), insulation temperature rating (60 °C / 75 °C / 90 °C), and the number of current-carrying conductors in the same raceway.

AWG	Cu 60 °C (A)	Cu 75 °C (A)	Cu 90 °C (A)	Al 75 °C (A)	Al 90 °C (A)
14	15	20	25	—	—
12	20	25	30	20	25
10	30	35	40	30	35
8	40	50	55	40	45
6	55	65	75	50	58
4	70	85	95	65	75
3	85	100	110	75	85
2	95	115	130	90	100
1	110	130	150	100	115
1/0	125	150	170	120	135
2/0	145	175	195	135	150
3/0	165	200	225	155	175
4/0	195	230	260	180	205

NEC 310.15(B)(3) requires a derating multiplier when more than three current-carrying conductors share a raceway. For 4–6 conductors, multiply the table ampacity by 0.80. For 7–9 conductors, use 0.70. For 10–20 conductors, use 0.50. This derating is separate from the ambient temperature correction described in the next section.

Temperature correction factors

Table 310.16 assumes a 30 °C ambient temperature. When you're running wire in an attic that reaches 50 °C in summer, or through a boiler room that runs hotter than 30 °C, you must apply a correction factor to the ampacity before selecting a gauge. The correction factor is applied to the base ampacity, not to the load current — which means a higher ambient temperature forces you to use a larger wire.

For 75 °C-rated copper in a 50 °C ambient: correction factor = √[(75 − 50) / (75 − 30)] = √[25/45] = √0.556 = 0.745. Multiply every ampacity in the 75 °C copper column by 0.745 before comparing to your load current. A 6 AWG copper conductor at 75 °C normally carries 65 A; in a 50 °C environment it's limited to 65 × 0.745 = 48 A.

For installations below 30 °C, the correction factor exceeds 1.0, allowing you to use a smaller wire than the base table suggests. Running wire in a 10 °C unheated space with 75 °C copper gives a factor of √[(75 − 10)/(75 − 30)] = √[65/45] = √1.444 = 1.202. That same 6 AWG conductor would handle 65 × 1.202 = 78 A in those conditions — though you'd rarely design to that limit in practice.

Worked example: sizing a 240 V, 30 A dryer circuit

A residential electric dryer is rated 5400 W at 240 V. The panel is 40 ft from the dryer outlet, and the cable will run through a conduit inside a 30 °C finished basement. The breaker will be a 30 A double-pole. Here's how to verify the wire size meets both ampacity and voltage-drop requirements.

Step 1 — Calculate the operating current. I = P / V = 5400 W / 240 V = 22.5 A. The circuit draws 22.5 A at full load.

Step 2 — Apply the 80% continuous load rule. Because household dryers cycle, this is not a continuous load (loads operating for 3 hours or more). No 125% upsize is required. The 30 A breaker and 30 A wire ampacity are acceptable for a 22.5 A load.

Step 3 — Check minimum NEC ampacity. For a 30 A circuit, NEC 240.4 requires wire rated at least 30 A. From Table 310.16, 10 AWG copper at 75 °C carries 35 A — sufficient. 10 AWG at 60 °C carries only 30 A, which is the absolute minimum but still technically meets code for a non-continuous load on a 30 A breaker.

Step 4 — Check voltage drop. NEC recommends keeping voltage drop under 3% for branch circuits. Round-trip wire length = 2 × 40 ft = 80 ft. Resistance of 10 AWG = 0.9989 Ω/1000 ft = 0.0799 Ω for 80 ft. Voltage drop = I × R = 22.5 A × 0.0799 Ω = 1.80 V. Percent drop = 1.80 / 240 = 0.75%. Well under 3% — 10 AWG passes voltage drop for this run length.

Step 5 — Final selection. 10 AWG copper with 75 °C insulation (NM-B cable or THHN in conduit) on a 30 A double-pole breaker. If the run were longer — say 120 ft — the voltage drop would climb to 2.25%, still acceptable at 75 °C but worth checking. At 200 ft the drop reaches 3.75%, which would require stepping up to 8 AWG.

Run your own numbers with the  — it handles both ampacity and voltage-drop checks simultaneously.

Copper vs aluminum conductors

Aluminum wire has roughly 61% of the conductivity of copper by volume, meaning an aluminum conductor must be one to two AWG sizes larger than copper to carry the same current. The NEC reflects this directly: 4 AWG copper at 75 °C carries 85 A, while 2 AWG aluminum at 75 °C carries 90 A. Aluminum is about one-third the weight of copper and costs significantly less per foot, which is why aluminum is standard for large feeders, service entrances, and utility distribution.

For branch circuits and small loads, copper remains dominant in residential wiring for practical reasons. Aluminum expands and contracts more than copper with temperature cycling, which can loosen connections over time. Aluminum also oxidizes on contact with air, forming a resistive oxide layer that increases connection resistance unless anti-oxidant compound is applied. NEC 110.14 requires using terminals rated for aluminum when terminating aluminum conductors — standard residential devices labeled "CO/ALR" are rated for both materials.

In commercial and industrial panel feeders, aluminum is common above 1/0 AWG. At those sizes, the weight and cost savings dominate and proper termination practices are more reliably followed. The heat load from a large aluminum feeder running at rated ampacity will differ from copper — use the  to estimate conductor heat dissipation for HVAC load analysis in electrical rooms.

Wire gauge applications by typical use case

Knowing the NEC table values is only part of the picture. Each gauge range has a practical domain where it appears most often, and understanding that context helps you catch specification errors quickly.

4/0 through 1/0 AWG copper: service entrances, large motor feeders, main panel feeds in residential and light commercial construction. These conductors are stiff, require large conduit (typically 1.5 in–2 in trade size), and are almost always installed in parallel runs for larger services.

1 AWG through 4 AWG: sub-panel feeds, HVAC equipment circuits, EV charging circuits at 80 A–100 A, and industrial machinery. 2 AWG copper at 75 °C handles 115 A, making it a common choice for 100 A sub-panels with short runs.

6 AWG through 10 AWG: the workhorses of residential electrical. 6 AWG on 60 A circuits (ranges, EV chargers), 8 AWG on 40 A circuits (dryers, water heaters), 10 AWG on 30 A circuits. THHN in conduit or NM-B cable are both standard here.

12 AWG and 14 AWG: general-purpose residential branch circuits. 12 AWG on 20 A circuits (kitchen, bathroom, general purpose), 14 AWG on 15 A circuits (lighting, bedroom outlets). Note that 14 AWG is not permitted on 20 A circuits — the breaker must match the wire's minimum ampacity.

16 AWG through 22 AWG: lighting fixtures, appliance cords, extension cords, low-voltage control wiring, and automotive wiring. 18 AWG is the standard gauge for thermostat wire (18/5 or 18/8 for modern smart thermostats).

24 AWG through 40 AWG: signal and data applications. 24 AWG is the standard for telephone and CAT3 cable. 26 AWG for patch cables and some CAT5e. 28–30 AWG for ribbon cables, PCB jumpers, and precision instrument wiring. 36–40 AWG for transformer windings, relay coils, and fine winding applications where conductor weight matters more than resistance.

For steel wire and structural cable applications where you need load-bearing wire properties rather than electrical properties, see the .

Skin effect and AC resistance

The resistance values in this article are DC resistance at 20 °C. For AC systems — which includes all power distribution — skin effect causes current to concentrate near the conductor surface rather than distributing uniformly across the cross section. This increases the effective resistance above the DC value, and the effect becomes more pronounced at higher frequencies and larger conductor sizes.

For conductors below 2 AWG at 60 Hz, the skin effect correction is less than 1% and you can safely ignore it. For 4/0 AWG copper at 60 Hz, AC resistance is approximately 1.5% higher than DC resistance. For 500 kcmil conductors, the difference reaches 5–8%. IEEE Standard 835 provides detailed AC resistance factors for large power cables.

At high frequencies — audio circuits, RF applications, switching power supplies — skin effect becomes the dominant factor. A 10 AWG wire designed for 60 Hz power works perfectly well at 60 Hz but has an effective AC resistance at 100 kHz roughly 30 times its DC resistance. High-frequency applications use Litz wire (multiple thin strands individually insulated) to defeat skin effect by forcing current to distribute evenly across many small conductors.

FAQ

What AWG is standard household wiring?

Most residential branch circuits use either 14 AWG (15 A circuits) or 12 AWG (20 A circuits). Kitchen and bathroom circuits are required by NEC to be 20 A, so 12 AWG is standard there. Lighting circuits are often 15 A with 14 AWG. The main service entrance is typically 4/0 AWG or 2/0 AWG copper for 200 A residential services.

How many amps can 12 AWG wire carry?

Under NEC Table 310.16, 12 AWG copper with 75 °C insulation carries 25 A in a raceway at 30 °C ambient. However, it is always protected by a maximum 20 A breaker per NEC 240.4(D). The 20 A breaker trips before the wire reaches its thermal limit, which is the protective design intent. Never install a 25 A breaker on a 12 AWG circuit.

What is the difference between AWG and metric wire sizes?

Metric wire sizes are specified directly by cross-sectional area in mm². The conversion is straightforward: find the mm² area from the AWG table, then match to the nearest metric size. Common equivalents: 2.5 mm² ≈ 13.3 AWG (closest is 12 AWG at 3.31 mm²); 4.0 mm² ≈ 11.5 AWG (closest is 10 AWG); 6.0 mm² ≈ 9.7 AWG (closest is 10 AWG). IEC 60228 is the international standard for metric conductor sizes.

Why does higher AWG number mean smaller wire?

AWG numbering originated from the wire drawing process. To produce thinner wire, you draw the stock through successively smaller dies — more draws means a thinner result. The gauge number originally corresponded to the number of drawing steps, so more draws (higher number) produced finer wire. The system has been formalized mathematically since then, but the inverse relationship persists.

Can I use aluminum wire for branch circuits?

Aluminum branch circuit wiring (15 A and 20 A circuits) was common in US residential construction from roughly 1965–1973. It was later linked to connection failures and fires due to improper terminations, thermal cycling, and galvanic corrosion where aluminum contacts copper or brass terminals. Current NEC code allows aluminum on branch circuits only with CO/ALR-rated devices. Most inspectors and electricians recommend against it for 15 A and 20 A branch circuits; aluminum remains standard and code-compliant for feeders 30 A and larger.

What gauge wire is used for EV charging?

A Level 2 EV charger at 240 V/48 A (11.5 kW) requires 6 AWG copper on a 60 A breaker, accounting for the 80% continuous load rule: 48 A / 0.80 = 60 A breaker minimum. The wiring itself needs to be rated for 60 A, which is 4 AWG at 60 °C or 6 AWG at 75 °C. For a 32 A / 7.7 kW charger (the most common Level 2 unit), 8 AWG copper on a 40 A breaker is sufficient. Run length matters — check voltage drop for runs over 50 ft.

How do I convert AWG to mm or mm²?

To convert AWG to diameter in mm: d(mm) = 0.127 × 92^((36−AWG)/39). To get cross-sectional area in mm²: A(mm²) = π/4 × d². For quick reference, 10 AWG = 2.588 mm diameter = 5.26 mm², and 12 AWG = 2.053 mm = 3.31 mm². These formulas work for any AWG value including the /0 sizes — substitute AWG = −1 for 1/0, −2 for 2/0, −3 for 3/0, and −4 for 4/0.

Sources: NEC 2023 (NFPA 70), NEC Table 310.16 for ampacity values; ASTM B3 Standard Specification for Soft or Annealed Copper Wire; IEEE Std 835-1994 Standard Power Cable Ampacity Tables; NIST Handbook 44 for conductor resistance at 20 °C; IEC 60228:2004 for metric conductor cross-sections. ``` --- 📍 v15.5.3 | main | 2026-04-01 10:42 ET | 0 modified | main only 🔋 ~18K used / ~982K left (of 1M context) — Coder (Sonnet 4.6)