Free PCB trace width calculator
PCB Trace Width Calculator: Current Capacity per IPC-2221
Find the minimum trace width for a given current, temperature rise and copper weight on internal and external layers, plus resistance, voltage drop and power loss.
Calculator
Trace width calculator.
Minimum width, external layer
- Internal layer width
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- Resistance (external)
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- Voltage drop
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- Power loss
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IPC-2221 curve fit: I = k·ΔT^0.44·A^0.725 (k = 0.048 external, 0.024 internal). IPC-2152 is less conservative for many internal traces. Add margin for high-reliability designs.
Quick table
Typical widths for 10 °C rise (external, IPC-2221).
| Current | 1 oz copper | 2 oz copper |
|---|---|---|
| 1 A | ≈ 12 mil | ≈ 6 mil |
| 2 A | ≈ 31 mil | ≈ 15 mil |
| 3 A | ≈ 54 mil | ≈ 27 mil |
| 5 A | ≈ 109 mil | ≈ 54 mil |
| 10 A | ≈ 283 mil | ≈ 142 mil |
IPC-2221 vs 2152
Which standard should you use?
IPC-2221 is the classic, conservative chart. IPC-2152 (2009) adds board thickness, copper planes and material conductivity, and it often allows narrower internal traces. For high-current designs, also consider heavy copper or a metal core PCB.
Understanding the results
Understanding the results.
The calculator returns the minimum cross-section needed to keep temperature rise within your limit for the given current, then converts it to width for your copper weight. Internal traces need roughly 2.6 times the width of external traces because they cannot shed heat to air. Resistance, voltage drop and power loss are worked out from the trace length and copper resistivity at the operating temperature.
Copper weight and current
Copper weight and current capacity.
| Copper weight | Thickness | Width for 3 A, 10 °C rise (external) |
|---|---|---|
| 0.5 oz | 17.5 µm | ≈ 108 mil |
| 1 oz | 35 µm | ≈ 54 mil |
| 2 oz | 70 µm | ≈ 27 mil |
| 3 oz | 105 µm | ≈ 18 mil |
Limitations
Limitations of the calculator.
IPC-2221 curves come from older test data and are conservative for many internal traces. They ignore nearby copper planes, board thickness and material conductivity, all of which IPC-2152 accounts for. They also assume a single isolated trace. Use the result as a safe starting point, add margin for high ambient temperatures or enclosed products, and use thermal simulation for high-current designs.
Worked examples
Worked examples.
A 2 A supply rail on an outer 1 oz layer with a 10 °C rise needs about 31 mil. The same current on an inner layer needs about 80 mil. Move it to 2 oz copper and the outer width drops to about 15 mil. For a 10 A motor feed on 2 oz outer copper, expect about 140 mil, or split the current across a plane and several vias.
Design tips
Trace width design tips.
- Use 10 °C rise for general designs; 20–30 °C only with thermal analysis
- Widen traces or add planes rather than relying on one narrow trace
- Account for vias: each via has its own current limit
- Heavier copper raises minimum trace/space — see copper thickness guide
FAQ
Tool questions.
How wide should a PCB trace be for 1 A?
About 12 mil (0.3 mm) on an external 1 oz layer for a 10 °C rise per IPC-2221.
Why are internal traces wider?
Internal traces cool less effectively, so IPC-2221 uses half the k constant, requiring about 2.6× the cross-section.
Is this trace width calculator free?
Yes, free and browser-based.
IPC-2221 or IPC-2152?
IPC-2221 is the classic conservative curve; IPC-2152 includes planes, thickness and material effects and often allows narrower internal traces.
Do vias limit current too?
Yes, each via has its own current limit; use several vias for high-current transitions.
What temperature rise should I use?
10 °C is a common default; 20–30 °C only with thermal analysis and adequate margin.
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