Language: EN
Trace width calculator (IPC-2221)
A track carrying current heats up. This calculator gives the width that keeps the temperature rise below your limit, using the IPC-2221 formula, for an outer and an inner layer side by side. It also gives the resistance of the track, the voltage it drops and the power it turns into heat.
Results
| Value | Outer layer | Inner layer |
|---|---|---|
| Width (mm) | – | – |
| Width (mil) | – | – |
| Resistance (mΩ) | – | – |
| Voltage drop (mV) | – | – |
| Power loss (mW) | – | – |
How it’s calculated
IPC-2221 gives the current a track can carry from its copper cross-section A, in square mils, and the temperature rise ΔT. The resistance uses the resistivity of copper at the track’s temperature (ambient plus rise).
A = (I / (k · ΔT^0.44))^(1 / 0.725) A in mil², I in A, ΔT in °C
k = 0.048 on outer layers, 0.024 on inner layers
W = A / t t = copper thickness in mil (1 oz = 1.378 mil = 35 µm)
ρ = 1.724 · 10⁻⁸ Ω·m · (1 + 0.00393 · (T − 20 °C))
R = ρ · L / (W · t) ΔV = I · R P = I² · RKeep its limits in mind.
- IPC-2221 comes from measurements made in the 1950s. Its newer replacement, IPC-2152, is more accurate and often allows inner tracks almost as narrow as outer ones. IPC-2221 stays on the safe side.
- Nearby copper planes, vias, other hot tracks and the board thickness all change how heat escapes. They aren’t included.
- The track is taken as one long, straight, isolated track at a constant current.
- Use more width than the minimum when you can. It costs nothing on most boards and lowers the voltage drop too.