PCB Trace Width, Via Current & Microstrip Impedance Calculator
IPC-2221 trace width and current, via capacity, resistance, voltage drop and microstrip impedance · free, no signup
See PCB Trace Width, Via Current & Microstrip Impedance Calculator in action
Free PCB Trace Width, Via Current & Impedance Calculator
Choosing a trace width should not be guesswork: too narrow and the trace overheats or drops too much voltage, too wide and you waste board space. This calculator uses the IPC-2221 relationship I = k·ΔT^0.44·A^0.725 to find the minimum width for a current, temperature rise, copper weight and layer position (external or internal), and the reverse — the current a given width can carry. It also shows the resistance, voltage drop and power loss over the trace length at your operating temperature, and a practical width with a 25% margin.
Further tabs estimate the current capacity and resistance of a plated via from its hole size and plating thickness, and the characteristic impedance of a microstrip from its width, height, copper thickness and dielectric constant using the IPC-2141 approximation. The IPC-2221 data is conservative for modern boards with copper planes; IPC-2152 and your manufacturer's stack-up tool give more precise figures for critical designs.
Key features
Width from current
IPC-2221 for external and internal layers, 0.5–3 oz copper.
Current from width
Maximum current for a chosen width and temperature rise.
Voltage drop and power
Resistance, drop and heat for the actual trace length.
Via and impedance tabs
Via capacity/resistance and microstrip Z₀ estimate.
How to use it
- Pick the tab and enter current, rise and copper weight.
- Read the minimum width and the practical width with margin.
- Check the voltage drop and power loss.
- Use the via and impedance tabs where relevant.
Worked example
Example
1 A on an outer layer of 1 oz copper with a 10 °C rise needs about 0.30 mm (11.8 mil); 3 A needs about 1.37 mm; a 0.25 mm trace carries about 0.9 A.
Who uses this tool
Electronics designers
Size power traces quickly.
Students
Learn the current-width relationship.
Makers
Check hobby boards before ordering.
Tips for the best results
- Use external layers for high current — they cool better.
- Add a margin: use 25–50% wider than the minimum.
- Use several vias in parallel for power paths.
- For controlled impedance use your fab's stack-up calculator.
Common mistakes to avoid
- Using internal-layer values for outer traces (too wide) or the reverse (too narrow).
- Ignoring voltage drop on long traces.
- Treating the microstrip estimate as exact.
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Frequently asked questions
What temperature rise should I use?
10 °C is common; 20–30 °C for tolerant designs.
What is 1 oz copper?
35 µm (1.378 mil) thick.
Is IPC-2221 still valid?
It is conservative; IPC-2152 is more accurate.
Is it free?
Yes.