Which temperature column should I use?

Use the column matching your conductor's insulation rating: 60 °C for TW and UF, 75 °C for THW and THWN, 90 °C for THHN and XHHW-2. However, the final ampacity is limited by the lowest-rated termination, which is usually 60 °C for circuits 100 A and below and 75 °C above that.

What ambient temperature is the base table?

Table 310.16 ampacities assume a 30 °C (86 °F) ambient. For any other ambient the tool applies the Table 310.15(B)(1) correction factor for the conductor's temperature rating, which can sharply reduce ampacity in hot attics or rooftops.

When do bundling adjustment factors apply?

When more than three current-carrying conductors share a raceway or cable, Table 310.15(C)(1) requires an adjustment: 80 percent for 4 to 6, 70 percent for 7 to 9, 50 percent for 10 to 20, and so on. The tool multiplies this against the ambient factor automatically.

Why is aluminum blank for small wire sizes?

Table 310.16 does not list aluminum conductors below 12 AWG because they are not used at those sizes in practice. The tool shows a dash for aluminum entries that have no published value.

Can I use the 90 °C column for the final size?

You may use 90 °C ampacities as the starting point for derating calculations, but the terminated ampacity is still capped by the equipment termination rating. The 90 °C value is rarely the usable number on its own.

What is the NEC 310.16 Full Ampacity Table Lookup?

Searchable NEC Table 310.16 ampacity reference from 14 AWG to 2000 kcmil, copper and aluminum, at 60, 75, and 90 °C ratings, with live ambient-temperature and conductor-bundling derate factors applied. A field reference for electricians. Runs in your browser. It runs free in your browser on Gera Tools, with nothing uploaded.

NEC 310.16 Full Ampacity Table Lookup

Name: NEC 310.16 Full Ampacity Table Lookup
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

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NEC Table 310.16 is the most-used table in the code book, and carrying it in a pocket reference saves time on every install. This tool reproduces the full table from 14 AWG through 2000 kcmil for both copper and aluminum across all three temperature columns, and applies live ambient and bundling derates.

How it works

Each conductor size has three published ampacities, one per insulation rating. The usable ampacity after corrections is:

adjusted ampacity = table value × ambient factor × bundle factor

The ambient factor comes from NEC Table 310.15(B)(1) based on the conductor’s temperature rating, and the bundle factor from Table 310.15(C)(1) based on the count of current-carrying conductors:

≤3 conductors → 1.00      4–6 → 0.80
7–9  → 0.70               10–20 → 0.50
21–30 → 0.45              31–40 → 0.40

Worked example with derating

A 4/0 AWG copper THWN conductor at 75 °C carries 230 A at the base 30 °C ambient with three or fewer current-carrying conductors. Move it into a 40 °C ambient (a hot attic, for example) with six current-carrying conductors in the same conduit:

Ambient correction factor for 75 °C insulation at 40 °C: approximately 0.88
Bundle adjustment for six conductors: 0.80
Adjusted ampacity: 230 × 0.88 × 0.80 ≈ 162 A

That is nearly 30% less than the table value. Ignoring derating factors is one of the most common sizing errors in residential and commercial work.

Choosing the right temperature column

The three temperature columns in 310.16 correspond to insulation classes:

Column	Insulation types	When to use
60 °C	TW, UF	Rarely for new work; wet or damp locations
75 °C	THW, THWN, RHW	Most commercial and industrial wiring
90 °C	THHN, XHHW-2, RHH	Starting point for derating; often limited by terminals

The practical rule: use 75 °C for most termination-limited circuits (equipment rated 60 °C for 100 A and below; 75 °C above 100 A per NEC 110.14(C)). You may use the 90 °C column as the base value for derating calculations, but if the derated result would exceed the 75 °C column value for that size, you are still limited by the terminal rating. In practice, THHN in conduit is almost always evaluated against the 75 °C column at the termination point.

Why aluminum has no entries below 12 AWG

Table 310.16 does not publish ampacities for aluminum conductors smaller than 12 AWG because such conductors are not used in practice for wiring — aluminum expands and contracts more than copper, and the terminations on small devices are not designed for it. The tool displays a dash for these blank entries rather than interpolating a value.

Notes

Always remember that the final breaker and lug termination rating still caps the result: a 75 °C-rated termination limits you to the 75 °C column no matter how the conductor is insulated. Verify against the adopted NEC edition in your jurisdiction, since ampacity tables have been revised across code cycles.