Stripline Impedance Calculator

A stripline is a copper trace buried between two ground planes inside a PCB — controlling its impedance is critical for high-speed signal integrity. Enter your Trace Width (W), Trace Thickness (T), Substrate Height (H), and Dielectric Constant (εr) into the Stripline Impedance Calculator to find the Characteristic Impedance in ohms. Secondary outputs include Capacitance per Unit Length, plus the W/(H-T) and T/H geometry ratios that indicate whether your dimensions fall within the formula's accuracy limits.

mil

Width of the stripline trace

mil

Thickness of the copper trace

mil

Distance between ground planes

Relative permittivity of substrate material

Results

Characteristic Impedance

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Capacitance per Unit Length

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W/(H-T) Ratio

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T/H Ratio

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Frequently Asked Questions

What is a stripline transmission line?

A stripline is a flat conductor embedded between two parallel ground planes, typically used in multilayer PCBs. The trace is completely surrounded by dielectric material and reference planes, providing excellent signal isolation and controlled impedance.

What are the accuracy limitations of stripline impedance calculators?

Analytical formulas work best when W/(H-T) < 0.35 and T/H < 0.25. For very thin or wide traces outside these ranges, the calculator may deviate significantly from actual values. Field solvers provide more accurate results for complex geometries.

How does dielectric constant affect stripline impedance?

Higher dielectric constant (εr) reduces the characteristic impedance. Common PCB materials like FR-4 have εr around 4.0-4.5, while high-frequency materials like Rogers can range from 2.2 to 10.

What trace width should I use for 50-ohm impedance?

The required trace width depends on substrate height, thickness, and dielectric constant. For typical FR-4 (εr=4.0) with 15 mil substrate height and 1.37 mil thickness, approximately 10-12 mil width achieves 50 ohms.

When should I use stripline instead of microstrip?

Use stripline when you need better signal isolation, reduced crosstalk, and symmetric field distribution. Stripline provides better EMI shielding but requires more PCB layers compared to microstrip.

How do I convert between different units (mil, mm, inches)?

Common conversions: 1 mil = 0.0254 mm, 1 inch = 1000 mils = 25.4 mm. Most PCB design tools work in mils for trace dimensions, but metric units are also widely used in modern designs.

What is the difference between symmetric and asymmetric stripline?

Symmetric stripline has equal spacing to both ground planes, while asymmetric stripline has unequal spacing. This calculator assumes symmetric configuration where the trace is centered between the planes.