Wire Gauge (AWG) Amperage Chart: How to Read It

Last updated: June 15, 2026

An ampacity chart tells you how many amps a given wire size can safely carry under specific conditions. But the table has three temperature columns, separate sections for copper and aluminum, and a set of fine-print conditions that determine whether the numbers even apply to your installation. This guide walks through how to read the chart correctly — and when to let the calculator do the lookup for you.

What "Ampacity" Actually Means

Ampacity is the maximum continuous current a conductor can carry without exceeding its temperature rating. It is not a fixed property of a wire size — it depends on the conductor material, its insulation's temperature rating, the ambient temperature around it, and how many other current-carrying conductors are bundled with it. NEC 2023 (NFPA 70) Table 310.16 codifies the most common scenario: insulated conductors in raceway or cable, no more than three current-carrying conductors, at a 30°C (86°F) ambient.

If your installation deviates from those baseline conditions — a hot attic, a crowded conduit, an outdoor run — the table values must be adjusted before you can use them. The wire size calculator handles standard ampacity lookup; for derated or unusual conditions, consult a licensed electrician.

The Three Temperature Columns

Table 310.16 has three columns: 60°C, 75°C, and 90°C. These refer to the conductor's insulation temperature rating, not the ambient air temperature. Common insulation types and their ratings include:

• 60°C: TW, UF (older or wet-location types)
• 75°C: THW, THWN, RHW — the most common types in general wiring
• 90°C: THHN, THWN-2, XHHW-2 — the most heat-tolerant insulation

The column you can actually use is constrained by NEC 110.14(C), which limits you to the temperature rating of the lowest-rated termination on the circuit — typically the breaker lug or wire connector. In most residential and light-commercial work, terminations are rated for 75°C (circuits over 100 A) or 60°C (circuits 100 A and under with standard equipment). Even if you pull 90°C THHN wire, you will generally size it to the 75°C column because that is what the breaker terminal is rated for.

Common AWG Ampacity Reference (NEC 2023 Table 310.16)

The table below re-expresses values from NEC 2023 Table 310.16 for commonly used wire sizes, as reported by multiple electrical reference sources as of 2026 (sources: wireref.com, ExpertCE). This is a reference summary — it is not the official NEC table. Always verify against the current edition of NFPA 70 and your local authority having jurisdiction (AHJ) before making wiring decisions.

† NEC 240.4(D) caps overcurrent protection for small copper conductors at 15 A (14 AWG), 20 A (12 AWG), and 30 A (10 AWG), regardless of the table ampacity shown above. Highlighted columns (Cu 75°C / Al 75°C) are most commonly applied in practice. Re-expressed from NEC 2023 Table 310.16 — verify against the official NFPA 70 document and your local AHJ before any wiring work.

Copper vs. Aluminum: What the Numbers Show

Copper carries more current than aluminum at the same AWG. Looking at the 75°C column, a 4 AWG copper conductor generally has a higher ampacity than 4 AWG aluminum — you need to go up roughly one to two AWG sizes in aluminum to match the same ampacity as copper (per NEC Table 310.16). This is why aluminum feeders and service entrance conductors are typically sized larger than their copper equivalents.

Aluminum also has a higher electrical resistivity than copper, which means greater voltage drop per foot at the same current. For long runs, this difference matters more than it does on short branch circuits. The copper vs. aluminum guide covers the trade-offs — cost, weight, termination requirements, and where each material is commonly used — in more detail.

What the Table Does Not Cover

The baseline Table 310.16 conditions are often not what you actually have. Before applying any ampacity value, confirm whether your installation requires:

• Ambient temperature correction — If the conductor runs through a space hotter than 30°C (an attic, a boiler room, outdoor conduit in a hot climate), NEC Table 310.15(B)(1) correction factors reduce the usable ampacity.
• Conduit fill / bundling adjustment — More than three current-carrying conductors in a raceway requires applying adjustment factors from NEC 310.15(C)(1). See the temperature and conduit derating guide for worked examples.
• Continuous load rule — Per NEC 210.20(A), if a load runs for three or more continuous hours, size the wire and breaker at 125% of the load current. EV charger circuits are always treated as continuous loads per NEC Article 625.42.
• Local AHJ amendments — Your local authority having jurisdiction may have adopted a different NEC edition or local amendments that affect these values.

Let the Calculator Apply the Rules for You

Reading a chart and applying the right column is straightforward for standard conditions. For anything involving long runs, voltage-sensitive equipment, or continuous loads, the calculation gets layered quickly. The wire size calculator applies ampacity from the 75°C copper or aluminum column, applies the 125% continuous-load multiplier when selected, and calculates voltage drop — then recommends the larger of the two resulting wire sizes. Enter your load, run length, material, and voltage, and it handles the lookup.

Related Guides

• How to size electrical wire — step-by-step walkthrough of the full sizing process
• Copper vs. aluminum wire — cost, ampacity, and termination trade-offs
• Temperature and conduit derating — applying NEC correction and adjustment factors
• Voltage drop explained — why long runs need a larger wire than ampacity alone requires