PCB Trace Width Calculator (IPC-2221)
By Santaji GadepatilinUpdated October 27, 2026
A copper track on a circuit board heats up as current flows through it, so it must be wide enough for the current it carries. The IPC-2221 formula links current, temperature rise and track size; for vias, see this guide to PCB via current capacity. This free PCB trace width calculator solves for whichever value you leave blank and shows the formula and steps.
How to use the PCB trace width calculator
Enter the current, the allowed temperature rise above ambient, the copper weight and whether the trace is on an external or internal layer. You get the required cross-section and minimum width in millimetres and mils.
For more background, read Controlled Impedance PCB Traces.
The IPC-2221 formula
I = k × ΔT0.44 × A0.725
with A in square mils, k = 0.048 for external layers and 0.024 for internal layers. Width = A ÷ (1.378 × copper oz).
Trace width for 1 oz copper, 10 °C rise
| Current | External layer | Internal layer |
|---|---|---|
| 0.5 A | 0.12 mm (5 mil) | 0.30 mm (12 mil) |
| 1 A | 0.30 mm (12 mil) | 0.78 mm (31 mil) |
| 2 A | 0.78 mm (31 mil) | 2.03 mm (80 mil) |
| 3 A | 1.37 mm (54 mil) | 3.56 mm (140 mil) |
| 5 A | 2.77 mm (109 mil) | 7.19 mm (283 mil) |
| 10 A | 7.19 mm (283 mil) | 18.71 mm (737 mil) |
Copper weights
| Copper | Thickness |
|---|---|
| 0.5 oz | 17.5 µm |
| 1 oz | 35 µm |
| 2 oz | 70 µm |
| 3 oz | 105 µm |
Doubling copper weight roughly halves the width needed.
Other checks
- Voltage drop: long, thin traces drop voltage. 1 oz copper has about 0.5 mΩ per square.
- Vias: a standard 0.3 mm via carries roughly 1–2 A; use several vias in parallel for high currents.
- Spacing: high-voltage traces need clearance and creepage per IPC-2221 or IEC 60664.
Frequently asked questions
How wide should a PCB trace be for 1 A?
On an outer layer with 1 oz copper and a 10 °C rise, IPC-2221 gives about 0.3 mm (12 mil). Inner layers need about 2.6 times the width.
Why do inner layers need wider traces?
Inner layers are surrounded by FR-4, which conducts heat poorly, so they cannot shed heat as well as outer layers.
What does 1 oz copper mean?
1 ounce of copper spread over 1 square foot — a thickness of about 35 µm (1.378 mil).
Is IPC-2221 accurate?
It is conservative for most designs. The newer IPC-2152 standard uses more detailed data that accounts for planes and board thickness.