Wire Ampacity Calculator

About this calculator

A wire's current-carrying capacity, or ampacity, can be estimated as I = J·A, where J is the current density the conductor material can safely sustain (typically a few amperes per square millimeter for copper, lower for aluminum) and A is the wire's cross-sectional area. Real-world ampacity tables (such as those in the NEC or IEC standards) refine this basic relationship further by accounting for insulation type, ambient temperature, and how many conductors are bundled together, since heat dissipation — not just raw cross-section — ultimately limits safe current.

Electricians use ampacity calculations to select the correct wire gauge for a circuit so it doesn't overheat or pose a fire risk, electrical engineers use it when designing power distribution systems and sizing conductors for motors or panels, and DIY homeowners doing wiring projects use it as a starting reference before checking official code tables for their exact installation conditions.