PCB Trace Width Calculator
Calculate the recommended PCB trace width based on current, copper thickness, and acceptable temperature rise using IPC-2221.
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.