PCB Impedance Calculator

Controlled impedance is critical in high-speed PCB design — a mismatch between trace impedance and the rest of the signal path causes reflections, signal loss, and timing errors. The PCB Impedance Calculator lets you select a trace type (Microstrip, Stripline, Edge Coupled, and more) and choose whether to solve for Calculated Impedance or Required Trace Width. Enter your trace width, trace thickness, substrate height, and dielectric constant to get your result, along with the effective dielectric constant and differential impedance for coupled pairs.

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For differential pairs only

Results

Calculated Impedance

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Required Trace Width

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Effective Dielectric Constant

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Differential Impedance

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Frequently Asked Questions

What is PCB impedance and why is it important?

PCB impedance is the resistance to AC current flow in a trace. Controlled impedance is crucial for signal integrity in high-speed digital circuits, preventing reflections and ensuring proper signal transmission.

What's the difference between microstrip and stripline?

Microstrip traces are on the surface of the PCB with dielectric on one side and air on the other. Stripline traces are embedded between dielectric layers, providing better isolation but slightly higher loss.

How accurate are these impedance calculations?

These calculations provide good approximations based on IPC-2141 standards. For critical applications, use field solver software or consult your PCB manufacturer for precise stackup calculations.

What dielectric constant should I use for FR4?

Standard FR4 has a dielectric constant (εᵣ) of approximately 4.3-4.5 at 1 MHz. High-frequency applications may require low-loss materials with different εᵣ values.

When do I need differential impedance?

Differential impedance is used for differential pairs like USB, Ethernet, or high-speed digital signals. Common values are 90Ω, 100Ω, or 120Ω depending on the application.

What trace width should I start with?

For 50Ω single-ended traces on standard FR4, start with 8-10 mil width. For 100Ω differential pairs, start with 5-6 mil width and 5-6 mil spacing.

How does trace thickness affect impedance?

Thicker traces have lower impedance. Standard PCB copper is 0.5 oz (0.7 mil) or 1 oz (1.4 mil). Thicker copper reduces impedance and improves current carrying capacity.