Two solve directions
Start from a current spec to get the required width, or from a routed width to check how much current it can carry.
Current Capacity Workspace
PCB Trace Width Calculator
A free PCB trace width calculator built on the IPC-2221 curve fit: enter current, copper weight, and allowed temperature rise to get the required width in mil or mm, plus trace resistance, voltage drop, and power loss. Runs entirely in your browser — no signup.
- Current→width or width→current
- External and internal layer factors
- Resistance, drop, and loss included
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Layer-aware results
Internal traces shed heat poorly, so the internal factor makes the required width roughly 2.6× larger at the same rise.
Full electrical readout
Every answer includes cross-section, DC resistance at operating temperature, voltage drop, and I²R loss.
Questions about stackup or heavy copper? Email [email protected]
Trace width calculator
IPC-2221 curve fit · results update as you type
Solve direction
Width unit
Results
- Required width
- 0.30 mm · 11.8 mil
- Current capacity
- 1.00 A
- Cross-section
- 16.3 mil² · 0.0105 mm²
- Trace resistance
- 42.7 mΩ
- Voltage drop
- 42.7 mV
- Power loss
- 42.7 mW
IPC-2221 is intentionally conservative. IPC-2152 usually allows more current — especially on internal layers — and vias, connectors, and a warm enclosure all need margin on top of this number.
Send this spec for review →Method
How the trace width calculation works
IPC-2221 relates current to conductor temperature through a single curve fit: I = k · ΔT^0.44 · A^0.725, where A is the trace cross-section in mil² and k is 0.048 for external traces and 0.024 for internal ones.
The solve runs in two steps. The formula is first inverted to get the required cross-section A = (I / (k·ΔT^0.44))^(1/0.725); that area is then divided by the copper thickness — 1 oz is about 1.378 mil — to produce the width. Resistance, voltage drop, and power loss follow from that geometry using the copper resistivity 1.7e-6 Ω·cm and a 3.9e-3/°C temperature coefficient.
For impedance-controlled routing the same width must also satisfy the stackup geometry — verify it with our impedance calculator
Layers
External vs internal traces
External traces shed heat through convection and radiation; internal traces sit inside laminate that conducts heat away less effectively. IPC-2221 encodes this as a halved k factor, so an internal trace needs about 2.6 times the width of an external trace for the same current and temperature rise.
In practice that makes internal power pours, planes, and polygon pours attractive: they offer a wide, cool current path without consuming routing channels.
Standards
IPC-2221 vs IPC-2152
IPC-2221 carries forward the IPC-D-275 chart, which was built conservatively from a limited data set. IPC-2152 is the newer standard, based on thermal testing that accounts for board thickness, copper planes, and material conductivity.
IPC-2152 usually permits more current for the same width — most noticeably on internal layers, where the old chart was pessimistic by design. Use this calculator for a conservative first pass, then check IPC-2152 or run a thermal model when the margin matters.
Reference
Trace width vs current at ΔT = 10 °C
Required trace width by current, copper weight, and layer — computed live from the same IPC-2221 fit as the calculator.
| Current (A) | 1 oz external | 2 oz external | 1 oz internal | 2 oz internal |
|---|---|---|---|---|
| 0.5 | 0.12 mm (4.5 mil) | 0.06 mm (2.3 mil) | 0.30 mm (11.8 mil) | 0.15 mm (5.9 mil) |
| 1 | 0.30 mm (11.8 mil) | 0.15 mm (5.9 mil) | 0.78 mm (30.8 mil) | 0.39 mm (15.4 mil) |
| 2 | 0.78 mm (30.8 mil) | 0.39 mm (15.4 mil) | 2.03 mm (80.0 mil) | 1.02 mm (40.0 mil) |
| 3 | 1.37 mm (53.8 mil) | 0.68 mm (26.9 mil) | 3.56 mm (140.0 mil) | 1.78 mm (70.0 mil) |
| 5 | 2.77 mm (108.9 mil) | 1.38 mm (54.4 mil) | 7.19 mm (283.2 mil) | 3.60 mm (141.6 mil) |
| 10 | 7.19 mm (283.2 mil) | 3.60 mm (141.6 mil) | 18.71 mm (736.8 mil) | 9.36 mm (368.4 mil) |
Widths in mm, mil in parentheses.
Margin
Design margin checklist
The formula assumes a straight, isolated trace carrying steady current. Real boards need margin at these points:
- Vias carry current through a plated barrel roughly 1 oz thick — derate or use several in parallel above ~1 A.
- Connectors and press-fit pins have their own current ratings, usually lower than the trace's.
- Parallel traces share current unevenly when length or width differs; the short, wide path takes most of it.
- Ambient temperature inside the enclosure adds to the allowed rise — a 45 °C box halves a 10 °C budget.
- Current pulses and motor inrush exceed the average; size for the sustained portion or add copper, not for the nameplate mean.
- Adjacent copper planes pull heat away in real boards — that IPC-2152 credit does not exist in this model.
Scaling up
When to move to heavy copper
When the required width climbs past roughly 200 mil on 1 oz copper, the practical answer is thicker copper, not a wider trace. Two to four ounces halve to quarter the width at the same current.
Our heavy copper PCB process plates 2–6 oz features for power distribution and high-current rails — send the calculated width, current, and rise target with your RFQ. heavy copper PCB
Technical questions
Trace width calculator FAQ
What does a PCB trace width calculator do?
It converts a current requirement and an allowed temperature rise into the minimum copper trace width using the IPC-2221 curve fit, then reports the trace's resistance, voltage drop, and power loss.
Which formula does this trace width calculator use?
I = k·ΔT^0.44·A^0.725, with k = 0.048 for external and 0.024 for internal traces, A the cross-section in mil², and ΔT the allowed rise in °C — the same fit the IPC-2221 ampacity chart is drawn from.
Why do internal traces need more width?
Laminate removes heat less effectively than air, so IPC-2221 halves the current constant for internal traces. For the same current and rise that works out to about 2.6 times the external width.
Does trace length change the width result?
No — width depends only on current, copper weight, and allowed rise. Length feeds the resistance, voltage drop, and power loss outputs, which is why the calculator asks for it separately.
How does this compare to IPC-2152?
IPC-2152 is the newer, test-based standard and usually allows more current — especially on internal layers. IPC-2221 results are a conservative floor; if the width is tight, rechecking against IPC-2152 data is worthwhile.
When should I switch to heavy copper?
When the required width grows past about 200 mil on 1 oz, or when you already specify 3 oz or more. Thicker copper reduces width directly and usually costs less than dedicating extra routing area.
Is the calculator free, and does it store my inputs?
It is free, runs entirely in your browser, and sends nothing to a server. The results are design estimates, not a substitute for product-level thermal validation.
From calc to copper
Have the width. Need it built?
Send the calculated width, copper weight, and current target with your Gerbers — our engineers confirm stackup and etch compensation before fabrication.