Free JLCPCB Impedance Calculator
Estimate single-ended and differential impedance for common PCB traces before ordering from JLCPCB.
Formulas use fast IPC-style approximations. Always confirm final impedance with JLCPCB’s official stackup/engineering output.
What is a JLCPCB impedance calculator?
A JLCPCB impedance calculator helps you estimate trace impedance before manufacturing your board. If your design includes high-speed digital signals, RF traces, USB, HDMI, Ethernet, or differential pairs, controlled impedance is one of the most important PCB constraints.
This page gives you a practical calculator you can use quickly during early routing. It is especially useful when you are deciding if a certain width/spacing will land near 50Ω single-ended or 90Ω/100Ω differential.
How to use this calculator
1) Select geometry
Choose microstrip for top/bottom layer traces over a reference plane, or stripline for inner layer traces between planes.
2) Enter stackup and copper values
- Er: dielectric constant of your PCB material (FR4 often around 4.0–4.5, frequency dependent).
- Dielectric height: for microstrip, distance from trace to reference plane; for stripline, plane-to-plane separation used by the approximation.
- Trace width and copper thickness: these strongly influence impedance.
3) (Optional) Add spacing for differential pairs
If you enter spacing, the calculator estimates differential impedance. This is useful for interfaces like USB, LVDS, RS-485, CAN FD, and Ethernet pair routing.
4) Compare against your target
Enter target values (for example 50Ω and 100Ω) to instantly see percentage error. If the difference is too high, adjust width and spacing and recalculate.
Common impedance targets in real projects
- 50Ω single-ended: RF lines, clocks, many generic high-speed routes.
- 90Ω differential: USB differential pair routing in many designs.
- 100Ω differential: Ethernet, LVDS, PCIe-like and other high-speed balanced links.
JLCPCB-focused routing tips
Start from the fabricator stackup
For best results, begin with JLCPCB’s published stackup options for your board thickness and layer count. Different prepreg/core constructions can shift impedance significantly, even with the same width and spacing.
Keep return paths continuous
A perfect width calculation will still fail in practice if your return path is broken by plane splits or large voids. High-speed traces should reference a solid plane along the full route.
Avoid unnecessary layer transitions
Each via transition can add discontinuity and extra parasitics. Minimize via count on critical lines and use stitching ground vias when needed for cleaner return current behavior.
Use differential pair constraints in your CAD tool
Set pair width, spacing, and length matching rules directly in your PCB editor. This keeps routing consistent and reduces late-stage rework.
Limitations and best practice
This calculator is designed for speed and intuition during layout planning. It does not replace a full electromagnetic field solver or JLCPCB’s engineering confirmation. Material tolerance, etch compensation, solder mask effects, copper roughness, and frequency-dependent dielectric behavior can all move final impedance.
- Use this tool to get close quickly.
- Finalize using official fabrication impedance checks.
- For very high-speed or RF-critical work, run a 2D/3D field solver.
Quick takeaway
If you are designing controlled impedance PCBs at JLCPCB, a fast impedance calculator can save hours. Use it early, route with clear constraints, and then verify with the board house before production release. That workflow gives you both speed and confidence.