If you need to route controlled-impedance traces in Altium Designer, this quick calculator gives you a practical first-pass estimate for trace impedance. It supports microstrip, stripline, and differential microstrip so you can move faster when defining your PCB stackup and routing rules.
Impedance Estimator
Enter your stackup and geometry values in millimeters.
What this Altium impedance calculator is for
In PCB design, impedance control is about signal integrity. High-speed interfaces like USB, Ethernet, PCIe, DDR, and many RF paths depend on transmission lines with predictable impedance. If geometry changes, impedance changes, and reflections can increase.
This calculator helps you estimate line impedance quickly while you are deciding your stackup and rule constraints in Altium. It is ideal for planning, not final sign-off.
Typical target impedances
- 50 Ω single-ended — very common for RF and many digital clock/data lines.
- 90 Ω differential — common for USB differential pairs.
- 100 Ω differential — common for Ethernet, LVDS, and many SerDes links.
- 85 Ω differential — common in some PCIe channels depending on spec/context.
How to use this with Altium Designer
1) Build your stackup first
Open Layer Stack Manager and define dielectrics, copper thickness, and reference planes. Your calculator inputs should match these values as closely as possible.
2) Set routing rules
In Design Rules, set preferred trace width and differential pair gap/width based on your target impedance. The goal is to make physical constraints match the electrical target.
3) Confirm with your board fabricator
Your fabricator may use field solver tools and material libraries that differ from generic formulas. Final impedance sign-off should always come from the fab’s controlled-impedance stackup recommendation.
Input definitions (quick reference)
- Er: Relative dielectric constant of the material around the trace.
- W: Trace width.
- T: Copper thickness.
- H: Distance from trace to reference plane (microstrip).
- B: Distance between two reference planes (stripline).
- S: Gap between differential pair traces (edge-to-edge).
Practical design tips
- Keep return paths continuous under high-speed traces.
- Avoid sudden neck-downs and large via stubs where possible.
- Route differential pairs with consistent gap and matched lengths.
- Do not mix impedance targets on one net class unless intentional.
- Treat this calculator as an estimate and lock final values with your fab notes.
Limitations to remember
Closed-form formulas are fast, but they simplify reality. Solder mask, copper roughness, weave effects, etch profile, and frequency-dependent dielectric behavior can all move real-world impedance away from idealized numbers. For production-critical designs, use your PCB vendor’s impedance tables or a full-wave solver.
Bottom line
This page gives you a practical, Altium-friendly starting point for impedance planning. Use it to choose reasonable trace geometry, then align those values with your stackup and manufacturer constraints before release.