The Wire Ampacity Calculator returns the allowable current of a conductor after applying the base ampacity (NEC 310.16 or IEC) and derating for ambient temperature and the number of bundled current-carrying conductors.
Wire Ampacity Calculator (NEC / IEC)
Calculate allowable ampacity for a wire using NEC 310.16 or IEC tables, with ambient temperature and conductor-count derating for copper and aluminum.
Inputs
Result
--
allowable ampacity (A)
--
base ampacity (A)
About Wire Ampacity Calculator (NEC / IEC)
Features
- NEC 310.16 and IEC tables
- Copper and aluminum
- Ambient temperature correction
- Conductor-count adjustment
How to Use
- Pick standard, material, rating and wire size.
- Set ambient temperature and conductor count.
- Read the allowable ampacity.
Examples
Example: 10 AWG copper, 75C, 30C ambient, 3 conductors -> 35 A. At 40C with 6 conductors -> 35 x 0.87 x 0.80 = 24.4 A.
Benefits
- Apply code derating correctly
- Compare copper vs aluminum
Frequently Asked Questions
What is ampacity?
Ampacity is the maximum current a conductor can carry continuously without exceeding its temperature rating.
Which table is used?
NEC 310.16 for the US/Canada, or IEC 60364-style values internationally. Pick the standard that applies to your project.
Why derate for ambient heat?
Higher ambient temperatures reduce the margin before the conductor overheats, so the allowable current drops.
Why derate for many conductors?
Bundled conductors share heat. NEC reduces ampacity when more than three current-carrying conductors are grouped.
Is my data saved?
No. All math runs in your browser.