AWG Current Capacity (Ampacity)

Quick-reference tables for common copper wire sizes. Ampacity depends on insulation temperature rating, ambient temperature, number of current-carrying conductors (bundling), and installation conditions.

How to Use

  1. Find your wire gauge (AWG).
  2. Choose the temperature column that matches your insulation rating (60°C / 75°C / 90°C).
  3. Derate if wires are bundled, in a hot area, or in an engine compartment.
  4. For 12V/24V systems, also check voltage drop (wire length matters).
Safety note: This page is a reference. Always follow applicable codes/standards (NEC/ABYC/SAE) and manufacturer specs for your exact wire type, insulation, and environment.

Quick Picks (Rule-of-Thumb)

These are common “mental math” picks people use for basic planning—verify against the tables and your actual conditions.

14 AWG: small loads / lighting 12 AWG: 20A-class circuits 10 AWG: 30A-class circuits 8 AWG: 40–50A class (varies) 4 AWG: high-current feeds 1/0–4/0: battery / winch class

NEC Copper Ampacity Reference (30°C ambient)

Values below are copied from NEC Table 310.15(B)(16) / 310.16 (formerly 310.16), for copper, with not more than three current-carrying conductors, based on 30°C (86°F) ambient.

Important: Overcurrent protection rules can still limit smaller conductors (see NEC notes).
If your ambient is hotter than 30°C, or you have more conductors, you must derate.
AWG 60°C (A) 75°C (A) 90°C (A)
14152025
12202530
10303540
8405055
6556575
4708595
385100115
295115130
1110130145
1/0125150170
2/0145175195
3/0165200225
4/0195230260

Source: NEC Table 310.15(B)(16) / 310.16 excerpt. (Copper ampacities shown; aluminum differs.)

Practical Notes (Chassis / Marine / Automotive)

1) Chassis vs. Building Wiring

Automotive and marine wiring often runs in hot compartments, looms, and tight bundles, which can reduce allowable current. Use standards that match your environment (ABYC for boats, SAE for automotive) rather than only building-wire tables when applicable.

2) Bundling = Derating

If multiple current-carrying conductors are run together in a loom/bundle, heat can transfer between them and ampacity should be derated. ABYC guidance explicitly calls this out for marine looms.

3) “SAE wire” size caveat

Some automotive “SAE” primary wire can have slightly different conductor area compared to the same AWG label, which affects current capacity. When in doubt: check the manufacturer datasheet for conductor area (circular mil / mm²) and insulation temperature rating.

Tip: For 12V systems, voltage drop is often the real enemy. Even if ampacity is “okay,” long runs can make devices unhappy.
If you want, I can add a companion page: “Voltage Drop (12V/24V) Quick Chart.”

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FAQ

Is ampacity the only thing that matters?

No. You also need to consider voltage drop, insulation temperature rating, ambient temperature, and bundling/loom conditions.

Can I use NEC ampacity for automotive wiring?

NEC tables are for specific building-wire installation assumptions. For vehicles/boats, use SAE/ABYC guidance and manufacturer specs— or derate conservatively.

Why do charts disagree online?

Many charts assume different insulation ratings, allowable temperature rise, airflow, bundling, and duty cycle. Always confirm the assumptions behind a chart before using it.

Page Info

Last updated:

Updates may include additional tables (aluminum, marine engine-room columns), voltage-drop references, and clearer derating examples.