---
title: "Microstrip and Stripline PCB Impedance Calculator"
description: "Calculate PCB trace characteristic impedance for microstrip and stripline layouts using trace width, substrate height, and dielectric constant."
image: "https://onlineminitools.com/tools/pcb-impedance-calculator/logo.svg"
---

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# PCB Impedance Calculator

Calculate PCB trace characteristic impedance for microstrip and stripline layouts using trace width, substrate height, and dielectric constant.

      O M T

## Why PCB Trace Impedance Matters

High-speed signals need a matched characteristic impedance along the transmission path. Microstrip routes on an outer layer above a ground plane; stripline routes an inner layer between two planes. Both depend on trace geometry and dielectric material.

## Microstrip Impedance

For a surface trace over a reference plane, a common approximation is:

 $$Z_0 = \frac{60}{\sqrt{\varepsilon_{eff}}} \ln\left(\frac{8h}{w} + \frac{w}{4h}\right)$$

when $w/h \le 1$, and a wider-trace form when $w/h > 1$. Here $w$ is trace width, $h$ is substrate height, and $\varepsilon_{eff}$ is the effective dielectric constant.

## Stripline Impedance

 $$Z_0 = \frac{60}{\sqrt{\varepsilon_r}} \ln\left(\frac{1.9 \times 2b}{0.8w + t}\right)$$

$b$ is distance from the trace to one ground plane, $t$ is copper thickness, and $\varepsilon_r$ is the laminate dielectric constant. FR-4 is often about 4.2 to 4.5.

Related tools: [PCB Trace Width Calculator](https://onlineminitools.com/pcb-trace-width-calculator), [Cable Impedance Calculator](https://onlineminitools.com/cable-impedance-calculator), and [Impedance Matching Calculator](https://onlineminitools.com/impedance-matching-calculator).

## Frequently Asked Questions

   **What impedance should I target?**

Many digital and RF boards use 50 Ω single-ended lines. USB and some buses use 90 Ω differential pairs built from two matched traces.

   **Microstrip or stripline?**

Microstrip is easier to probe and route on outer layers. Stripline gives better shielding and more stable fields because the trace sits between planes.

   **Which dielectric constant should I enter?**

Use the laminate value from your fab notes. FR-4 is commonly about 4.3, but it varies with resin content and frequency.

   **Does copper thickness change impedance much?**

For typical microstrip widths it is a second-order effect. Stripline formulas include thickness more directly in the effective width term.

   **Is this a substitute for a field solver?**

No. Analytic formulas are good for quick estimates. Final high-speed designs should still be checked with stackup-specific field solvers or fab guidance.

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### Recent Visits

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