PCB Capacitance Calculator
Calculate the parasitic capacitance for PCB traces.
Results:
Parasitic Capacitance:
About this Calculator:
This PCB Capacitance Calculator helps you calculate the parasitic capacitance for PCB traces. By providing the trace width, trace length, dielectric thickness, and dielectric constant, you can determine the parasitic capacitance. This tool is essential for engineers working on high-frequency designs where parasitic capacitance can affect signal integrity.
How to Use:
Enter the trace width (mm), trace length (mm), dielectric thickness (mm), and dielectric constant. Click "Calculate" to see the parasitic capacitance. Use the "Reset" button to clear the inputs and start over.
Equation Used:
The parasitic capacitance is calculated using the formula:
\[ C = \frac{\epsilon \cdot A}{d} \] where: \[ \epsilon \text{ is the dielectric constant, } A \text{ is the area of the trace, and } d \text{ is the dielectric thickness.} \]
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This gives wrong/misleading results. The dielectric constant in the calculator shows example "4.5" which makes one believe it to be the relative dielectric constant (permittivity), but turns out the calculator expects to get the absolute dielectric constant. Absolute dielectric constant is never 4.5, it's usually around 0.04 pF/mm for PCBs.
Thank you for your feedback. To clarify, the calculator is designed to use the **relative dielectric constant (εr)**, which is the standard convention in PCB and transmission line calculations. For FR4, this value is typically around 4.2–4.8, so the example value of 4.5 is indeed the **relative permittivity**.
The **absolute permittivity** (ε = εr × ε₀) would be about 0.04 pF/mm for FR4, but since ε₀ is a known physical constant, calculators usually only require the relative value (dimensionless). I’ll update the calculator label/documentation to make it clear that the input is εr (relative permittivity), to avoid any confusion.