ENGINEERING TOOLS

ISO 9001:2015

AWG Wire Gauge Calculator

Wire gauge conversion, NEC current rating, and voltage-drop sizing — copper & aluminum, metric & imperial.

A free reference calculator for wire-and-cable engineers. American Wire Gauge (AWG) is the standardized system for conductor diameter — a smaller AWG number means a thicker wire. Use the tools below to convert AWG to metric, look up NEC current rating (ampacity), or size a conductor to a voltage-drop limit.

Convert

AWG ↔ diameter, area (mm², kcmil, circular mils) and resistance — in both directions.

Current rating

Ampacity by 60 / 75 / 90 °C insulation class with live ambient & bundling derating.

Size a wire

Smallest standard gauge that meets your voltage-drop limit over a given run length.

Direction

Wire gauge

AWG

Conductor

Result

—

AWG wire size chart (diameter, area, resistance & ampacity)

Reference values for solid copper conductors. Diameter and area follow ASTM B258; resistance is DC at 20 °C; ampacity columns are NEC NFPA 70 Table 310.16 (≤3 conductors, 30 °C ambient).

AWG	Ø mm	Ø in	Area mm²	kcmil	Ω/km (Cu)	60 °C A	75 °C A	90 °C A
4/0	11.684	0.4600	107.2193	211.60	0.16	195	230	260
3/0	10.405	0.4096	85.0288	167.81	0.20	165	200	225
2/0	9.266	0.3648	67.4309	133.08	0.26	145	175	195
1/0	8.251	0.3249	53.4751	105.53	0.32	125	150	170
1	7.348	0.2893	42.4077	83.69	0.41	110	130	145
2	6.544	0.2576	33.6308	66.37	0.51	95	115	130
3	5.827	0.2294	26.6705	52.63	0.65	85	100	110
4	5.189	0.2043	21.1506	41.74	0.82	70	85	95
5	4.621	0.1819	16.7732	33.10	1.03	—	—	—
6	4.115	0.1620	13.3018	26.25	1.30	55	65	75
7	3.665	0.1443	10.5488	20.82	1.63	—	—	—
8	3.264	0.1285	8.3656	16.51	2.06	40	50	55
9	2.906	0.1144	6.6342	13.09	2.60	—	—	—
10	2.588	0.1019	5.2612	10.38	3.28	30	35	40
11	2.305	0.0907	4.1723	8.23	4.13	—	—	—
12	2.053	0.0808	3.3088	6.53	5.21	20	25	30
13	1.828	0.0720	2.6240	5.18	6.57	—	—	—
14	1.628	0.0641	2.0809	4.11	8.28	15	20	25
15	1.450	0.0571	1.6502	3.26	10.45	—	—	—
16	1.291	0.0508	1.3087	2.58	13.17	—	—	—
17	1.150	0.0453	1.0378	2.05	16.61	—	—	—
18	1.024	0.0403	0.8230	1.62	20.95	—	—	—
19	0.912	0.0359	0.6527	1.29	26.41	—	—	—
20	0.812	0.0320	0.5176	1.02	33.31	—	—	—
21	0.723	0.0285	0.4105	0.81	42.00	—	—	—
22	0.644	0.0253	0.3255	0.64	52.96	—	—	—
23	0.573	0.0226	0.2582	0.51	66.78	—	—	—
24	0.511	0.0201	0.2047	0.40	84.21	—	—	—
25	0.455	0.0179	0.1624	0.32	106.18	—	—	—
26	0.405	0.0159	0.1288	0.25	133.90	—	—	—
27	0.361	0.0142	0.1021	0.20	168.84	—	—	—
28	0.321	0.0126	0.0810	0.16	212.90	—	—	—
29	0.286	0.0113	0.0642	0.13	268.47	—	—	—
30	0.255	0.0100	0.0509	0.10	338.53	—	—	—
31	0.227	0.0089	0.0404	0.08	426.88	—	—	—
32	0.202	0.0080	0.0320	0.06	538.28	—	—	—
33	0.180	0.0071	0.0254	0.05	678.76	—	—	—
34	0.160	0.0063	0.0201	0.04	855.91	—	—	—
35	0.143	0.0056	0.0160	0.03	1079.28	—	—	—
36	0.127	0.0050	0.0127	0.03	1360.94	—	—	—
37	0.113	0.0045	0.0100	0.02	1716.12	—	—	—
38	0.101	0.0040	0.0080	0.02	2163.98	—	—	—
39	0.090	0.0035	0.0063	0.01	2728.73	—	—	—
40	0.080	0.0031	0.0050	0.01	3440.87	—	—	—

How it works — formulas & references

Geometry

d(mm) = 0.127 · 92^((36−n)/39)

Diameter and area (π/4·d²) follow ASTM B258. IEC 60228 defines the equivalent metric conductor classes.

Resistance

R = ρ · L / A (ρ at 20 °C)

Resistance is DC at 20 °C — copper ρ=1.724×10⁻⁸ Ω·m, aluminum 2.826×10⁻⁸ Ω·m. For large conductors at 60 Hz, AC resistance is slightly higher due to skin effect. IEC 60228 defines equivalent metric conductor classes.

Ampacity

NEC 310.16 × ambient × bundling

NEC NFPA 70 Table 310.16, with 310.15(B) ambient and 310.15(C) bundling derating. IEC 60364-5-52 for metric installations.

Worked example — size a wire for voltage drop. Carry 15 A over a 5 m one-way run at 12 V DC, copper, max 3 % drop:

Allowed drop = 3 % × 12 V = 0.36 V
Allowed resistance = 0.36 V ÷ (2 × 15 A × 5 m) = 0.0024 Ω/m (k = 2 for DC round-trip)
Smallest gauge at or below that → 8 AWG (2.06 Ω/km = 0.00206 Ω/m); 10 AWG (3.28 Ω/km) is too thin
Actual drop at 8 AWG = 2 × 15 × 0.00206 × 5 = 0.31 V (2.6 %) ✓

Conversion check: 12 AWG copper → 2.053 mm Ø · 3.31 mm² · 5.21 Ω/km.

Results are reference estimates — verify against the applicable code and the authority having jurisdiction (AHJ) for any installation.

Sources

ASTM B258 — standard AWG dimensions
NEC NFPA 70, Table 310.16 & 310.15 — ampacity & derating
IEC 60228 — metric conductor classes
IEC 60364-5-52 — current-carrying capacity & installation

Reviewed by

MWMichael Wang, Senior Technical Engineer
TeleWire Technology · ISO 9001:2015 certified cable-assembly manufacturer
Last reviewed June 2026

AWG vs SWG vs metric (mm²)

Three systems describe the same wire — and the same gauge number is a different diameter in each. Always confirm which standard a spec uses.

AWG

American Wire Gauge — the US standard, defined by formula. A lower number means a thicker wire.

SWG

British / Imperial Standard Wire Gauge — a legacy fixed table that runs thicker than AWG for the same number.

Metric · mm²

IEC 60228 — states the actual conductor cross-section, which ultimately sets the current capacity.

Gauge #	AWG Ø mm	SWG Ø mm
16	1.291	1.626
18	1.024	1.219
20	0.812	0.914
22	0.644	0.711
24	0.511	0.559

Same number, different wire — SWG runs thicker than AWG. See the AWG guide for the full background.

Stranded vs solid conductors

Solid

Single solid conductor — smallest overall diameter
Lower cost; easy to terminate by IDC or in PCB holes
Best for permanent, static installations
Stiffer — can fatigue and break if repeatedly flexed

Stranded

Many fine strands — ~1.1–1.3× larger overall diameter
Same copper area & ampacity at the same AWG
Highly flexible — survives bending & vibration
Standard for cable assemblies, harnesses, robotics & drag-chain

Same AWG = same cross-section and current rating; stranded simply trades a slightly larger diameter for flexibility. It's specified as equivalent solid AWG plus a strand count — e.g. 22 AWG 7/30 = seven strands of 30 AWG.

Glossary

Ampacity: The maximum continuous current a conductor can carry without exceeding its temperature rating.
Circular mil (cmil): Area of a circle 0.001 in (one mil) in diameter — a US unit for conductor cross-section. 1 kcmil = 1,000 cmil.
Voltage drop: The loss of voltage along a conductor due to its resistance (V = k·I·R·L); typically kept under 3 % on a branch circuit.
Resistivity (ρ): A material's intrinsic opposition to current. Copper ≈ 1.724×10⁻⁸ Ω·m at 20 °C; aluminum ≈ 2.826×10⁻⁸.
Skin effect: At higher AC frequencies, current crowds toward the conductor surface, raising effective resistance above the DC value.
Derating: Reducing a conductor's rated ampacity for high ambient temperature or for bundling several current-carrying conductors together.

AWG calculator — FAQ

What is AWG?

American Wire Gauge (AWG) is the standard U.S. system for specifying solid round conductor diameter. A lower AWG number is a thicker wire — every 6 gauges roughly halves or doubles the cross-sectional area.

How do I convert AWG to mm²?

Compute the diameter with d(mm)=0.127·92^((36−n)/39), then area = π/4·d². For example, 12 AWG ≈ 2.05 mm diameter ≈ 3.31 mm². Use the Convert tab above for any gauge.

What is the ampacity of 12 AWG copper?

Per NEC Table 310.16, 12 AWG copper is rated 20 A at 60 °C, 25 A at 75 °C and 30 A at 90 °C insulation, before ambient and bundling derating.

Copper vs aluminum — how much bigger does aluminum need to be?

Aluminum has ~1.6× the resistivity of copper, so an aluminum conductor carries less current for the same gauge — typically you go up about two AWG sizes to match a copper conductor's ampacity.

How do I size wire for voltage drop?

Use the Size-a-wire tab: enter current, run length, system voltage and a maximum %-drop. It returns the thinnest standard AWG whose drop stays within your limit, using R=ρL/A round-trip.

Need this gauge in a custom cable assembly?

Once you've sized your conductor, TeleWire Technology builds it into a custom cable assembly or wire harness to IPC/WHMA-A-620 — prototype to production, made in Taiwan.

Request a Quote