Wire Gauge Amp Capacity Lookup

Manufacturer-sourced reference ampacities and a simplified voltage-drop estimate for copper and aluminum conductors.

Reference information only. Actual conductor and overcurrent-protection requirements depend on installation conditions and the electrical code adopted in your jurisdiction. Gauge alone does not determine a safe conductor or breaker.

Reference conditions

Conductor material

Reference temperature column

Reference condition: insulated conductors in raceway, cable, or earth; no more than three current-carrying conductors; 30°C ambient. Equipment/terminal markings and correction or adjustment factors can require a lower usable ampacity. A 90°C insulation rating alone does not authorize use of the 90°C value.

Conductor size

12 AWG copper · 75°C reference

25 A

Conductor ampacity reference — not a breaker rating.

Separate small-conductor overcurrent limit: 12 AWG copper is commonly limited to a 20 A overcurrent device under the small-conductor rule, subject to listed exceptions. This is separate from the 25 A tabular reference shown above.

Candidate reference size by ampacity only

Required ampacity (A)

This is a comparison against one selected reference column, not an automatic conductor recommendation. It does not perform a load calculation or account for terminals, derating, conductor use, overcurrent protection, or special rules.

Methodology, scope, and sources

Ampacity and resistance values come from Southwire product engineering data for copper XHHW-2, copper THHN/THWN-2, and aluminum XHHW-2 conductors. Southwire identifies the ampacity conditions as based on the 2023 NEC Table 310.16: insulated conductors in raceway, cable, or earth, no more than three current-carrying conductors, and 30°C ambient. The small-copper specification was updated April 22, 2026; the linked aluminum specification was updated January 7, 2026. The 60°C entries were cross-checked against Southwire’s published copper and aluminum 60/75/90°C engineering tables. NumPad does not reproduce an NEC table.

Temperature-column limitation. Equipment markings govern the usable termination temperature. UL’s public guides explain that a higher insulation temperature rating alone does not permit using a higher ampacity at a lower-rated terminal. See the UL Panelboards Guide, UL Circuit Breaker Guide, and UL Wire and Cable Guide.

Voltage drop. The calculator uses the manufacturer’s DC resistance at 25°C and the formulas shown in the calculator. The 3%/5% design guidance is described in NEC informational notes; it is not presented here as a universal mandatory threshold. See NFPA’s public 2025 NEC development materials.

Jurisdiction. NEC edition adoption and local amendments vary. Verify the adopted rules with the authority having jurisdiction; NFPA’s NEC enforcement maps provide general adoption context.

Primary data sources: 14–10 AWG copper, 8 AWG–500 kcmil copper, and 8 AWG–500 kcmil aluminum. Last verified: August 27, 2026.

How to use this reference

Start with the installation, not only the gauge. Identify the conductor or cable type, material, equipment temperature markings, ambient conditions, current-carrying conductor count, and applicable code edition before choosing a reference column.

Keep ampacity and overcurrent protection separate. A tabular ampacity is one input to a circuit design. Load calculations, small-conductor rules, continuous or nonlinear loads, motors, appliances, services, feeders, and listed equipment can introduce other requirements or exceptions.

Treat voltage drop as a planning estimate. It can help compare conductors under the same simplified assumptions, but it does not replace an engineering calculation for sensitive, long, large, or complex AC circuits.

Have a qualified electrician or engineer complete and verify the final design, and confirm it with the authority having jurisdiction.

Frequently Asked Questions — Wire Gauge Ampacity

How to interpret the reference data without treating it as a final circuit design.

No. Conductor ampacity and circuit overcurrent protection are related but separate checks. Breaker selection can depend on conductor size, equipment markings, load type, continuous-load rules, permitted exceptions, and the adopted code. This lookup intentionally does not produce a generic breaker recommendation.