PCB Design Tools
IMPEDANCE CALCULATOR
Calculate characteristic impedance for microstrip, stripline, CPWG, and differential pair transmission lines.
Calculate characteristic impedance for PCB transmission lines including microstrip, stripline, coplanar waveguide (CPWG), and edge-coupled differential pairs. Select your geometry, enter stackup parameters, and get impedance, propagation delay, and wavelength — all in real time.
Outer layer trace above a ground plane — most common for single-ended signals
Input Parameters
0.127 mm
0.102 mm
Used for wavelength and electrical length calculations
Results
Characteristic Impedance (Z0)
Effective εr
3.09
Prop. Delay
149.5 ps/in
Wavelength
6.72 in
@ 1.0 GHz
Elec. Length
53.80 °/in
@ 1.0 GHz
Microstrip Cross-Section
PCB Impedance Calculator Results — Microstrip
Generated by calpak-usa.com/Resources/PCB-Impedance-Calculator
| Geometry | Microstrip |
| Trace Width | 5.0 mil (0.127 mm) |
| Copper Weight | 1 oz (1.4 mil) |
| Dielectric Constant | εr = 4.20 |
| Dielectric Height | 4.0 mil (0.102 mm) |
| Characteristic Impedance | 54.67 Ω |
| Effective εr | 3.09 |
| Propagation Delay | 149.5 ps/in |
| Wavelength @ 1.0 GHz | 6.72 in |
| Electrical Length @ 1.0 GHz | 53.80 °/in |
Calculated using IPC-2141 / Wadell approximations. For reference only — always verify impedance with your PCB fabricator's stackup data and field solver.
Understanding PCB Impedance Control
Controlled impedance is critical for any PCB carrying high-speed digital signals or RF energy. When a signal's rise time is fast enough that the trace length exceeds roughly one-tenth of the signal wavelength, the trace behaves as a transmission line. Mismatched impedance causes reflections that degrade signal integrity, increase EMI, and can prevent reliable communication.
The characteristic impedance of a transmission line depends on its geometry and the dielectric properties of the surrounding material. A microstrip (trace on an outer layer above a ground plane) is the most common topology. Stripline (trace sandwiched between two ground planes) offers better shielding and lower radiation, making it preferred for sensitive inner-layer routing. Coplanar waveguide (CPWG) adds ground pours adjacent to the trace on the same layer, useful for RF circuits where via transitions must be minimized.
For differential signaling (USB, LVDS, PCIe, Ethernet), the differential impedance Zdiff depends on both the single-ended impedance Z0 and the coupling between the two traces. Tighter spacing increases coupling and reduces Zdiff. Common targets are 90Ω for USB 2.0/3.0 and 100Ω for Ethernet and PCIe.
The formulas in this calculator use IPC-2141 and Wadell approximations, which are accurate for typical PCB geometries. For critical applications — especially above 10 GHz or with exotic dielectrics — always verify with a 2D field solver and your PCB fabricator's actual stackup data. Calpak USA's engineering team can perform signal integrity analysis and impedance-controlled fabrication for aerospace and defense applications. Contact us for a design review.
Quick Reference: Common Impedance Targets
Typical FR-4 (εr = 4.2), 1 oz copper
| Application | Target Z | Geometry | Typical w / h |
|---|---|---|---|
| General single-ended | 50Ω | Microstrip | 8 mil / 4 mil |
| USB 2.0 / 3.0 | 90Ω diff | Diff. Microstrip | 5 mil / 4 mil / 5 mil gap |
| PCIe / Ethernet | 100Ω diff | Diff. Microstrip | 4 mil / 4 mil / 6 mil gap |
| DDR4 / DDR5 | 50Ω SE | Stripline | 4 mil / 10 mil b |
| RF / 50Ω CPWG | 50Ω | CPWG | 12 mil / 8 mil / 6 mil gap |
Values are approximate starting points for FR-4. Actual impedance depends on fabricator stackup, copper roughness, solder mask, and frequency. Always verify with your fabricator's impedance report.
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