PCB Trace Width Calculator

IPC-2221 gives the current a copper conductor carries for a temperature rise as I = k·ΔT^0.44·A^0.725, with A the cross-section in square mils and k = 0.048 for external layers (cooled by air) or 0.024 for internal layers (buried in laminate). Solved for A and divided by the copper thickness — 1 oz/ft² is 1.378 mil (35 µm) — it gives the minimum width. The fit was drawn from 1950s measurements on single traces in still air and is valid roughly for 0–35 A, 0.5–3 oz copper and rises of 10–100 °C; outside that range the page still calculates but says so.

With a length, the trace resistance is ρ·L ÷ A using copper's resistivity 1.724 × 10⁻⁸ Ω·m at 20 °C corrected by the 0.00393/°C coefficient to the operating temperature (ambient plus the allowed rise). Voltage drop is I·R and power loss I²·R. These are for the minimum width; a wider trace drops less, and on long power runs the drop, not the temperature, usually sets the width.

IPC-2152 (2009) replaced the generic curves with data that account for board thickness, copper planes, enclosure and altitude, and it generally allows narrower external traces than 2221 and wider internal ones. It is a licensed standard and is not reproduced here; the 2221 formula remains the public, conservative starting point most calculators use. Adjacent hot traces, vias and connectors need their own checks. Nothing leaves the browser; the same four anonymous usage counts as the rest of the site apply.