PCB Track Width Calculator (IPC-2221)

Calculate minimum PCB trace width based on current, temperature rise, and copper thickness

Input Parameters

Current (I)

Load current through the trace (0.01 - 200 A)

Temperature Rise (ΔT)

°C

Allowed temperature rise above ambient (1 - 100°C)

Copper Thickness

Standard PCB copper thickness

Layer Type

External Layer

Top or bottom layer with better heat dissipation (k = 0.048)

Internal Layer

Inner layer with reduced cooling (k = 0.024, requires wider traces)

Safety Margin (Optional)

Derating factor for additional safety (0 - 50%)

Enter parameters and click Calculate to see results

IPC-2221 Calculation Method

External Layers (Top/Bottom)

For traces on external layers (top or bottom of PCB), the IPC-2221 standard uses a higher constant due to better heat dissipation through convection and radiation.

The formula relates current to cross-sectional area and temperature rise through an empirical relationship.

I = k \cdot (\Delta T)^{0.44} \cdot A^{0.725}

Where:

I

= CurrentA

k

= IPC-2221 constant[-]

\Delta T

= Temperature rise°C

A

= Cross-sectional areamil²

W

= Trace widthmil

T

= Copper thicknessmil

Internal Layers

For traces on internal layers, heat dissipation is reduced because the trace is sandwiched between PCB layers. This requires wider traces for the same current.

The formula uses a lower constant (k = 0.024) compared to external layers, resulting in approximately 2.6× wider traces for the same conditions.

I = 0.024 \cdot (\Delta T)^{0.44} \cdot A^{0.725}

Where:

I

= CurrentA

k

= IPC-2221 constant[-]

\Delta T

= Temperature rise°C

A

= Cross-sectional areamil²

Solving for Trace Width

To calculate the required trace width W for a given current, we rearrange the formula:

Since A = W × T (cross-sectional area = width × thickness), we can solve for W:

W = \frac{1}{T} \left( \frac{I}{k \cdot (\Delta T)^{0.44}} \right)^{\frac{1}{0.725}}

Where:

W

= Trace widthmil

T

= Copper thicknessmil

I

= CurrentA

k

= Layer constant[-]

\Delta T

= Temperature rise°C

Copper Thickness Reference

0.5 oz:

17.5 µm (0.7 mil)

1.0 oz:

35 µm (1.4 mil)

2.0 oz:

70 µm (2.8 mil)

3.0 oz:

105 µm (4.2 mil)

Note: 1 oz copper means 1 ounce of copper per square foot of board area.

Understanding the Formula

Temperature Rise (ΔT): The formula is empirically derived from experiments. The exponent 0.44 represents the non-linear relationship between temperature and current capacity.

Cross-sectional Area: The exponent 0.725 (≈ 3/4) reflects how current capacity scales with area. Doubling the area does not double the current capacity due to skin effect and non-uniform current distribution.

Safety Margin: Adding a safety margin increases the effective current used in calculations, resulting in wider traces. This accounts for: aging, manufacturing variations, environmental factors, and unexpected current spikes.

Current Density: Typical safe range is 10-30 A/mm². Higher density increases temperature and reduces reliability. Lower density improves reliability but requires more board space.

Design Recommendations

General Rule: Use ΔT = 10°C for normal operation, ΔT = 20°C for higher reliability
High Current (>5A): Consider using thicker copper (2 oz or 3 oz)
Tight Spaces: Use external layers when possible for better heat dissipation
Critical Traces: Add 10-20% safety margin for power supply traces
Very Wide Traces: Consider using polygons or multiple parallel traces
Length Matters: Longer traces accumulate more heat - consider trace length in design