PCB trace width calculator
IPC-2221 estimate for current-carrying traces. Enter current, copper weight and allowed temperature rise, then pick the layer — width is shown in mil and mm.
Inputs
Results
Trace width
external layer, IPC-2221 model
Trace width
1 mil = 0.0254 mm
Min. pad suggestion
≈ 1.5× trace width — reference only
Area(mil²) = (I / (k × ΔT^b))^(1/c); width = area / copper_thickness_mil (1 oz ≈ 1.378 mil). The IPC-2221 model is a conservative approximation (±10% is normal) — confirm against your board house, derating, and any nearby traces before production.
About trace sizing
Trace width trades current capacity against board space and resistance. External layers dissipate heat into air roughly twice as well as internal planes, so internal traces need about 2.5–3× the width for the same current and temperature rise.
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Frequently asked questions
How is the required PCB trace width calculated?
The tool applies the IPC-2221 model I = k·ΔT^0.44·A^0.725 to find the copper cross-sectional area in mil², then divides by the foil thickness to get the width: area(mil²) = (I ÷ (k × ΔT^b))^(1/c), width = area ÷ thickness, with 1 oz copper ≈ 1.378 mil. For 1 A at a 10 °C rise on a 1 oz external layer the result is a few mil of width, shown in both mil and mm.
What is the difference between external and internal traces?
External layers dissipate heat into air roughly twice as well as internal planes, so the current coefficient k drops from 0.048 to 0.024 for internal traces and the same current needs about 2.5–3× the width. Choose the layer that matches your stack-up — the default is external.
How much wider should a pad be than the trace?
The tool suggests a minimum pad of about 1.5× the trace width as a reference. The IPC-2221 model is a conservative approximation — ±10% error is normal — so confirm the width against your board house, the allowed temperature rise (valid for 10–100 °C) and any nearby traces before production.
IPC-2221 is an approximation — verify against your board house, solder mask, ambient temperature and IPC-2152 data for critical designs. ICBOMS provides this tool for reference only.