🔌 PCB Trace Width Calculator

How the IPC-2221 Trace Width Formula Works

The IPC-2221 standard provides the industry-accepted method for calculating minimum trace width based on current carrying capacity and allowable temperature rise. The formula is:

I = k × ΔT^0.44 × A^0.725

Where I is current in Amperes, ΔT is temperature rise in °C, A is cross-sectional area in mils², and k is a constant (0.024 for internal traces, 0.048 for external traces). The cross-sectional area is trace width × copper thickness.

To solve for width: Width = (I / (k × ΔT^0.44))^(1/0.725) / thickness

Copper Weight vs. Thickness

• 0.5 oz: 0.7 mils (17.5 μm) — fine-pitch, high-density boards
• 1.0 oz: 1.37 mils (35 μm) — standard for most PCBs
• 2.0 oz: 2.74 mils (70 μm) — power traces, high current
• 3.0 oz: 4.11 mils (105 μm) — heavy copper, power supplies
• 4.0 oz: 5.48 mils (140 μm) — industrial, high current

FAQ

Why are external traces rated higher? External traces can dissipate heat into the air on one side, while internal traces are surrounded by insulating PCB material. This gives external traces approximately 2× the current capacity for the same width.

What temperature rise is safe? Most designs use 10°C rise for conservative, reliable operation. For cost-sensitive designs, 20°C is acceptable. Above 30°C may affect nearby components and accelerate aging.

Does this account for parallel traces or planes? No — this is for a single trace in isolation. If a trace runs over a ground plane, heat dissipation improves. If multiple high-current traces run parallel, they heat each other.

How do I calculate voltage drop? First calculate trace resistance using R = ρ × L / A, where ρ for copper is about 0.0172 Ω·mm²/m at 25°C. Then voltage drop is V = I × R.