PCB Trace Width Calculator
Calculate the required PCB trace width from current, temperature rise and copper weight per IPC-2221.
Per IPC-2221. Add margin for long traces, vias and dense boards.
Disclaimer: This calculator is provided for general informational and educational purposes only, on an “as is” basis and without any warranty of accuracy or fitness for a particular purpose. Results may contain errors — always verify independently before relying on them in real designs. PartAndStock accepts no liability for any loss or damage arising from use of this tool, including when embedded on third-party sites.
How to use
- 1Enter the current the trace will carry, in amperes.
- 2Enter the allowable temperature rise (typically 10 °C).
- 3Select the copper weight (1 oz ≈ 35 µm is most common).
- 4Select the layer (external/internal); the required width is shown in mm and mils.
How it works
Find the minimum width a PCB trace needs to safely carry a given current, based on the IPC-2221 standard.
How IPC-2221 works
When current flows through a trace, the copper's resistance heats it up. IPC-2221 gives, with an empirical formula, the current a trace can carry without exceeding a given temperature rise: it first computes the required cross-sectional area, then divides by the copper thickness to get the width. External (surface) layers shed heat to air better, so they need a thinner trace than internal layers (the k coefficient is twice as high).
Limits and margin
This formula only accounts for heating; it does not cover voltage drop along long traces. For long power rails, dense multilayer boards, via transitions and vibration/reliability, add margin to the calculated width. At high currents it is often more practical to use thicker copper (2–3 oz) or parallel traces / copper pours instead of a single wide trace.
Worked examples
- 1 A, ΔT 10 °C, 1 oz, external → ≈ 0.30 mm (11.8 mils)
- 3 A, ΔT 10 °C, 1 oz, external → ≈ 1.37 mm (53.8 mils)
- 1 A, ΔT 10 °C, 1 oz, internal → ≈ 0.79 mm (internal ~2× wider)
Current → Trace Width (1 oz · external · ΔT 10 °C)
| Current | Width | mils |
|---|---|---|
| 0.5 A | 0.12 mm | 4.6 |
| 1 A | 0.30 mm | 11.8 |
| 2 A | 0.78 mm | 30.8 |
| 3 A | 1.37 mm | 53.8 |
| 5 A | 2.77 mm | 108.9 |
| 10 A | 7.20 mm | 283.5 |