AWG Ampacity Calculator

Look up the cross-section and resistance of an American Wire Gauge size, the voltage drop over a run, and a guideline current-carrying capacity. Calculates in your browser.

NEC ampacity (copper, 60 °C)

-

Cross-section-
Resistance-
Voltage drop (round trip)-
Drop as % of supply-

Show the math

Voltage drop is the round-trip resistance times the current:

Vdrop = I × (Ω/1000 ft ÷ 1000) × 2 × length

Ampacity is the copper 60 °C column of NEC Table 310.16 (2017 edition Table 310.15(B)(16)): 30 °C ambient, no more than three current-carrying conductors in a raceway or cable. The 60 °C column is what the NEC uses for circuits of 100 A or less unless the equipment is listed for higher. The table starts at 14 AWG; smaller gauges are for electronics and cords, rated by other standards. Always follow your local electrical code for real installations. All math runs in your browser.

What this does

An AWG ampacity calculator looks up the cross-section and resistance of an American Wire Gauge size, works out the voltage drop over a run, and shows its NEC current-carrying capacity (copper, 60 °C column).

How to use it

  1. Select the AWG size.
  2. Read the cross-section.
  3. Check the resistance per length.
  4. See the NEC ampacity.

How it works

Each AWG step changes the diameter by a fixed ratio, so cross-section roughly doubles every three sizes. Ampacity is the copper 60 °C column of NEC Table 310.16 (30 °C ambient, up to three current-carrying conductors), the column used for circuits of 100 A or less; the table starts at 14 AWG.

Understanding your result

The ampacity shown is one NEC table column under stated conditions, not a rating for your installation: higher ambient temperatures, more conductors bundled together, or a different insulation rating all change the allowable current. Follow your local code and ask an electrician for real wiring.

Example

12 AWG copper is rated around 20 A in typical residential wiring.

Sources & methodology

Last updated .

Frequently asked questions

What is ampacity?

Ampacity is the maximum current a conductor can carry continuously before its temperature rating is exceeded. It depends on gauge, insulation, and installation.

Where do the ampacity values come from?

The copper 60 °C column of NEC Table 310.16 (Table 310.15(B)(16) in the 2017 edition), for 30 °C ambient and up to three current-carrying conductors. Your local code, derating factors, and equipment ratings still apply, so consult an electrician for real installations.

Is my data stored?

No. Everything is calculated locally in your browser.