PCB Trace Width Calculator

Follow the steps below to calculate the required trace width:

Inputs

• 1. Current (I): Enter the average current that the trace will carry, in Amps. This is the current flowing through the PCB trace.
• 2. Temperature Rise (∆T): Enter the temperature rise you want to allow, in °C. This is the difference between the trace temperature and ambient temperature.
• 3. Copper Thickness: Enter the copper thickness, in oz/ft². Standard values are 1 oz/ft², 2 oz/ft², etc. Higher values allow for higher current capacity.
• 4. Unit Selection: Choose whether you want the output in Metric (mm) or Imperial (mils) units for the trace width.

Formulas

1. Cross-Sectional Area Formula

The following formulas from IPC-2221 Section 6.2 are used to determine the cross-sectional area (A) of the trace for a given current, temperature rise, and copper thickness.

For internal traces (using constant \(k = 0.024\)):
\[ I = 0.024 \times ( ∆T)^{0.44} \times A^{0.725} \]

For external traces (using constant \(k = 0.048\)):
\[ I = 0.048 \times ( ∆T)^{0.44} \times A^{0.725} \]

Where:

• I = Maximum current in Amps
• ∆T = Temperature rise in °C
• A = Cross-sectional area of the trace in mils²
• k = Constant specific to the type of trace (0.024 for internal traces, 0.048 for external traces)

To calculate the cross-sectional area \(A\), we rearrange the formula:

\[ A = \left( \frac{I}{k \times ( ∆T)^{0.44}} \right)^{\frac{1}{0.725}} \]
Once we have the cross-sectional area \(A\), we can use it to calculate the trace width.

2. Trace Width Formula

To find the trace width from the cross-sectional area, we use the following formula:

\[ \text{Width (mils)} = \frac{A (\text{mils}^2)}{\text{Thickness (oz/ft²)} \times 1.378 (\text{mils/oz})} \]
Where:

• A = Cross-sectional area in mils²
• Thickness = Copper thickness in oz/ft²
• 1.378 is a constant used to convert the thickness from oz/ft² to the correct width units in mils.

3. Conversion from Mils to Millimeters

If you are calculating the trace width in Imperial units (mils) and need to convert it to Metric units (mm), use the following conversion factor:

\[ 1 \, \text{mil} = 0.0254 \, \text{mm} \]

Example Calculation

For an internal trace with the following parameters:

• Current \(I = 2 \, \text{A}\)
• Temperature Rise \( ∆T = 10 \, \text{°C}\)
• Copper Thickness = 1 oz/ft²
• Trace Length = 50 mm
• Desired units = Metric (mm)

First, calculate the cross-sectional area using the formula for internal traces:

\[ A = \left( \frac{I}{0.024 \times ( ∆T)^{0.44}} \right)^{\frac{1}{0.725}} = \left( \frac{2}{0.024 \times (10)^{0.44}} \right)^{\frac{1}{0.725}} \approx 208.21 \, \text{mils}^2 \]

Then, calculate the trace width using the trace width formula:

\[ \text{Width} = \frac{208.21}{1 \times 1.378} \approx 151.4 \, \text{mils} \approx 3.85 \, \text{mm} \]

Therefore, the trace width needed is approximately 3.85 mm.

Note: This calculator is based on IPC-2221 and We have tried our best to keep this calculator accurate, still We cannot take the guarantee of accuracy of the calculator.