PCB Trace Impedance & Width Calculator

PCB Trace Calculators assist in designing trace dimensions for target impedance matching or current carrying limits.

Formulas:

• Microstrip Impedance (IPC-2141): Z0 = (87 / sqrt(Er + 1.41)) * ln(5.98 * h / (0.8 * w + t))
• Trace Width for Current (IPC-2221): Area (sq mils) = (Current / (k * Temp_Rise^b))^(1/c), then Width = Area / (Thickness * 1.378)

Usage: Fill in the substrate dielectric constant, copper weight, and current to calculate matched impedance traces or high-current power rails.

When you need it: Sizing a PCB trace for a given current (by allowable temperature rise) or for a target controlled impedance, following the IPC-2221 rules.

Worked example: An IPC-2221 external trace in 1 oz copper carrying 2 A with a 10 °C rise needs about 0.5 mm of width; thicker copper or a smaller allowed rise lets you go narrower.

Tips & gotchas:

• Internal traces need roughly twice the width of external ones for the same current — they cool poorly.
• Copper weight (0.5/1/2 oz) sets the thickness that goes into the current calculation.
• Vias and connectors are thermal chokepoints; add copper or multiple vias where current concentrates.
• Current-carrying width and controlled-impedance width are separate goals — solve each, then take the wider.