What this calculator does
Every PCB copper trace heats up as current flows through it due to resistive losses. This calculator estimates the maximum current a trace can carry for a chosen temperature rise above ambient, using the widely used IPC-2221 empirical formula.
The formula
IPC-2221 gives I = k × ΔT^0.44 × A^0.725, where A is the trace’s cross-sectional area in square mils (width × copper thickness), ΔT is the allowed temperature rise in °C, and k is 0.048 for external (outer-layer) traces or 0.024 for internal traces, since internal traces are surrounded by insulation and dissipate heat less efficiently.
This is a widely used design estimate, not a guarantee — real current capacity also depends on board thickness, airflow, nearby heat sources, and copper purity, so leave margin for critical designs.