# PCB trace

According to recommendations in IPC-2221 (formerly IPC-D-275, MIL-STD-275) on how to calculate minimum PCB (printer circuit board) trace width.

Below table is valid for:

• PCB material FR-4
• Board thickness=1.6mm (0.063")
• Trace thickness=35µm (1 oz)
• Allowed temperature rise=10 °C

## Table

Current Width (inner) Width (outer)
A mils mils
0.010.3080.118
0.051.540.591
0.13.081.18
0.26.152.37
0.412.34.73
0.412.34.73
0.515.45.91
0.618.57.1
0.721.58.28
0.824.69.46
0.927.710.6
1.030.811.8

Note: 1 mil = 1/1000" = 0.0254 mm

## Graph

### Outer traces (0-1 A) ### Outer traces (1-10 A) ### Inner traces (0-1 A) ### Inner traces (1-10 A) ## Formula

Given:

• I [A] (Current)
• T [°C] (Temperature rise)
• m [oz] (Mass of PCB trace)

Constants:

• y = 1.378 [mils/oz] for copper
• b = 0.44
• c = 0.725
• k = 0.048 (for outer layers)
• k = 0.024 (for inner layers)

Formulas:

• A [mils²] = ${(\frac {I}Template:KT^b)}^{\frac {1}{c}}$ (PCB trace area)
• l [mils] = $\frac {A}{m y}$ (PCB trace width)