PCB Trace Width Calculator

PCB trace width must be wide enough to carry the target current without excessive temperature rise, which can damage the board or cause intermittent failures. The IPC-2221A standard provides the governing formula.

For External Traces (outer copper layers):

W = (I / (k × ΔT^b))^(1/c) / (T × 1.378)

Simplified using the IPC approximation:

Area (mils²) = (Current / (k × ΔT^0.44))^(1/0.725)

Where:

• k = 0.048 for external layers; 0.024 for internal layers
• ΔT = Allowable temperature rise in °C (typically 10°C for standard boards)
• Area is then converted to width by: Width (mils) = Area / (Thickness in mils)

Standard 1oz copper = 1.4 mils thick (35 µm). 2oz = 2.8 mils.

Worked Example — 3A trace on 1oz external copper, ΔT = 10°C:

• Area = (3 / (0.048 × 10^0.44))^(1/0.725)
• 10^0.44 ≈ 2.754 → 0.048 × 2.754 = 0.1322
• (3 / 0.1322)^(1/0.725) = (22.69)^1.379 ≈ 105 mils²
• Width = 105 / 1.4 = 75 mils (1.905 mm)

Quick Reference Table:

• 1A → ~10 mils (0.25 mm) external
• 2A → ~30 mils (0.76 mm) external
• 5A → ~120 mils (3.0 mm) external
• 10A → ~340 mils (8.6 mm) external

Safety note: Internal layers need ~2× wider traces for the same current due to reduced heat dissipation. Always add a 20% safety margin for high-reliability or automotive boards.