Trace Current Capacity (IPC-2221)

I = k × ΔT^0.44 × A^0.725

Calculator

Result
—

Formula

I = k × ΔT^0.44 × A^0.725

Description

The IPC-2221 standard provides an empirical formula for estimating the current-carrying capacity of PCB copper traces based on allowable temperature rise and cross-sectional area. The constant k differs for external (outer layer) and internal (inner layer) traces because external traces benefit from better convective cooling. Cross-sectional area is the product of trace width and copper thickness (typically 1 oz/ft² = 1.4 mil = 35μm). The formula is conservative and assumes standard FR-4 substrate with natural convection cooling.

Variables

  • I — Maximum current (A)
  • k — Layer constant: 0.048 for external, 0.024 for internal traces
  • ΔT — Allowable temperature rise above ambient (°C)
  • A — Trace cross-sectional area (mil²)

Practical Notes

For 1 oz copper (1.4 mil thick): a 10 mil wide trace has A = 14 mil², a 50 mil trace has A = 70 mil². At ΔT = 10°C on an external layer: 14 mil² carries about 0.5A, 70 mil² carries about 1.5A. For higher currents, use wider traces, heavier copper (2 oz = 2.8 mil), or polygon fills. The IPC-2152 standard provides updated, more accurate charts.

Related Formulas

Trace Resistance Trace Voltage Drop Via Current Capacity (IPC-2221) Microstrip Impedance Stripline Impedance Differential Pair Impedance

Need more features?

Save calculations, import telemetry data, simulate battery discharge, and collaborate with your team.

Try the App