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.

NEC 310.16 Full Ampacity Table Lookup

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

Notes and example

A 4/0 AWG copper THWN conductor at 75 °C carries 230 A at the base 30 °C, three conductors. Move it into a 40 °C ambient with six conductors and the usable ampacity drops to 230 × 0.88 × 0.80 ≈ 162 A. 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.