Trace Parameters
Peak continuous current through the trace.
Typical: 10°C (precision), 20°C (general), 40°C (high-power). IPC-2221 tests at 10°C and 20°C.
Copper Weight
Resistance (Optional)
Used for resistance calculation. IPC-2221 reference: 25°C.
Minimum Trace Width
External Layers (top / bottom)
Min Width
—
mm
Min Width (mils)
—
mil (1 mil = 25.4 µm)
Cross-section
—
mil²
Resistance
—
mΩ
Internal Layers
Min Width
—
mm
Min Width (mils)
—
mil
Cross-section
—
mil²
Resistance
—
mΩ
Voltage Drop & Power Dissipation
Ext Layer V drop
—
mV
Int Layer V drop
—
mV
Ext Layer Power
—
mW
Int Layer Power
—
mW
IPC-2221 Formula
This calculator uses the empirical IPC-2221 formulae (the same basis as most PCB design EDA tools).
/* Cross-section area (mil²): */
A = I / (k × ΔT^b) // IPC-2221 §6.2
/* External layers: k=0.048, b=0.44 */
/* Internal layers: k=0.024, b=0.44 */
/* Trace width (mm): */
width = A / (copper_oz × 1.378 × 39.37) // area / (thickness_mil × mm_per_inch)
/* Resistance (Ω): */
R = ρ_Cu × L / (w × t) // ρ_Cu = 1.72×10⁻⁸ Ω·m at 20°C
A = I / (k × ΔT^b) // IPC-2221 §6.2
/* External layers: k=0.048, b=0.44 */
/* Internal layers: k=0.024, b=0.44 */
/* Trace width (mm): */
width = A / (copper_oz × 1.378 × 39.37) // area / (thickness_mil × mm_per_inch)
/* Resistance (Ω): */
R = ρ_Cu × L / (w × t) // ρ_Cu = 1.72×10⁻⁸ Ω·m at 20°C
IPC-2221 provides conservative, empirically-derived minimums. Real boards with thermal relief or conformal coating may allow slightly narrower traces, but use the calculated minimum as your floor.
Copper Weight Reference
| oz/ft² | Thickness (µm) | Typical use | Fabrication notes |
|---|---|---|---|
| 0.5 oz | 17.5 µm | Signal layers in multilayer boards | Standard for HDI; lower crosstalk |
| 1 oz | 35 µm | General purpose — most 2–4 layer boards | Default at most PCB fab houses; no extra cost |
| 2 oz | 70 µm | Power planes, motor drives, high current | Specify at order; slight cost premium |
| 3 oz | 105 µm | Heavy power distribution | Limited fabricator support; longer lead time |
| 4 oz | 140 µm | Busbars, welding controllers, EV drives | Specialist fabricators; very high cost |