Wire Ampacity Chart
Simplified current associations next to common AWG sizes for home-shop questions. This is not a full NEC ampacity table — insulation type, temperature, and install method change the answer.
Reference only — not a wiring design tool. Verify with local code, product markings, and a licensed electrician when required. Disclaimer
| AWG | Dia. (in) | Dia. (mm) | Simplified ampacity note |
|---|---|---|---|
| 4/0 AWG | 0.4600 | 11.68 | Service entrance / large feeder conductor |
| 3/0 AWG | 0.4096 | 10.40 | Service entrance / large feeder |
| 2/0 AWG | 0.3648 | 9.27 | Service entrance / large feeder |
| 1/0 AWG | 0.3249 | 8.25 | Sub-panel feeder / large load |
| 1 AWG | 0.2893 | 7.35 | Sub-panel feeder / large load (conditions apply) |
| 2 AWG | 0.2576 | 6.54 | Large feeder (conditions apply) |
| 3 AWG | 0.2294 | 5.83 | Large feeder (conditions apply) |
| 4 AWG | 0.2043 | 5.19 | Feeder / high-load circuit (conditions apply) |
| 6 AWG | 0.1620 | 4.12 | Higher capacity runs (conditions apply) |
| 8 AWG | 0.1285 | 3.26 | Larger feeders / higher load (conditions apply) |
| 10 AWG | 0.1019 | 2.59 | Often associated with 30A copper (conditions apply) |
| 12 AWG | 0.0808 | 2.05 | Often associated with 20A copper branch (conditions apply) |
| 14 AWG | 0.0641 | 1.63 | Often associated with 15A copper branch (conditions apply) |
| 16 AWG | 0.0508 | 1.29 | Light duty extension / low current — no NEC ampacity rating |
| 18 AWG | 0.0403 | 1.02 | Low-current / lamp cord class — no NEC ampacity rating |
| 20 AWG | 0.0320 | 0.81 | Signal / electronics wire — no NEC ampacity rating |
Sample-length copper (12 AWG)
Weak commerce only — temporary/sample lengths, not feeder design. Confirm AWG and listing. Never size permanent circuits from a product card.
As an Amazon Associate we earn from qualifying purchases. Disclosure
Common branch-style scenes
These rows match the AWG tool scenes. They are educational associations for copper under typical talk-shop conditions — not a permit drawing.
-
15A branch-style question
Typical AWG: 14 AWG
Common residential copper association only — verify code, temperature, and install method.
-
20A branch-style question
Typical AWG: 12 AWG
Common residential copper association only — verify code, temperature, and install method.
-
30A-class load question
Typical AWG: 10 AWG
Many 30A copper applications use 10 AWG — not universal; check appliance and code.
How to read this chart
Find the AWG you are asking about, read the short note, then stop and check the product listing and code path. For a focused “20 amp” walkthrough, use what gauge wire for 20 amp. For temporary shop cords, length and load matter more than a single ampacity row — open the extension cord gauge helper.
Insulation type comparison
Ampacity changes a lot with insulation. The same 12 AWG copper carries different current depending on whether it is THHN in free air, THWN in a wet conduit, or older TW in a bundled cable. The notes in the chart above assume typical THHN/THWN for shop runs. For exact sizing, use the AWG / ampacity tool and pick the insulation rating your wire actually has.
-
THHN / THWN-2
90°C conductor rating, 75°C in wet locations. Most common for shop branch runs in conduit. Highest ampacity per gauge.
-
XHHW
90°C dry and wet. Common for feeder runs and service entrance. Similar ampacity to THHN/THWN-2.
-
TW
60°C rating. Older NM cable sheathing approximates this in some references. Lower ampacity per gauge — derate if you see TW or older NM without marked conductor temperature.
-
NM-B (Romex)
90°C conductor, but 60°C termination limit per code. The ampacity of NM-B is the 60°C column for the breaker size used.
Temperature derating
The numbers in this chart assume a 30°C (86°F) ambient. In a hot attic, a sun-baked conduit run, or near boiler piping, the conductor ampacity drops. Standard correction factors apply for ambient temperatures above 30°C, and adjustment factors apply when more than three current-carrying conductors share a raceway or cable.
- 36–40°C (97–104°F): multiply by 0.91 for 90°C insulation, 0.82 for 75°C.
- 41–45°C (106–113°F): 0.87 (90°C) or 0.71 (75°C).
- 46–50°C (115–122°F): 0.82 (90°C) or 0.58 (75°C).
- Bundling 4–6 conductors: multiply by 0.80. 7–9: 0.70. 10–20: 0.50.
A 12 AWG THHN rated 30A at 30°C drops to about 24A in a 40°C attic with five conductors in the conduit. That is the difference between a 30A and a 20A breaker decision. For these correction math problems, the AWG / ampacity tool applies the standard factors once you pick the insulation rating and bundle count.
FAQ
What does ampacity mean on this page?
Ampacity is how much current a conductor can carry under stated conditions. This chart only shows simplified shop associations next to each AWG — not a full code ampacity table by insulation, ambient temperature, or bundling.
Can I size house wiring from this chart alone?
No. Permanent branch circuits need local electrical code, listed products, and often a licensed electrician. Use this page for education and to prepare a better question for the AWG tool or a professional.
What is the common copper association for 20 amp?
Many US residential copper branch questions associate 20A with 12 AWG under typical conditions — always verify temperature rating, device listings, and code. Open the 20 amp decide page for a focused walkthrough.
How is this different from the wire gauge chart?
The gauge chart emphasizes diameter. This page emphasizes the short current-related note next to each AWG and the common branch scenes. Both are reference-only.
Sources
Diameter values follow common AWG copper tables. Ampacity notes are simplified educational associations — not a published code table. Always verify with the governing electrical code and product listings.
See the site disclaimer for limits of use.