50Ω Stripline Calculator
Controlled Impedance | FR-4 (Er=4.5) | IPC-2141
Quick answer
On FR-4 (εr 4.5) with 0.4 mm plane spacing and 1 oz copper, an isolated stripline line needs about 0.1185 mm (4.66 mil) width for 50 Ω, by the IPC-2141-style single-ended approximation used here.
How sensitive is that result?
| Nominal (w = 0.118 mm, εr = 4.5) | 50.0 Ω |
|---|---|
| Width +10 % | outside model domain |
| Width −10 % | 52.1 Ω |
| εr = 4.2 (same width) | 51.8 Ω |
| εr = 4.8 (same width) | 48.4 Ω |
Assumptions
- Single-ended isolated line; copper 0.035 mm; plane spacing 0.4 mm; εr 4.5.
- The sensitivity rows re-run the same production function with one input changed.
Limits
- This is not a differential-pair result and ignores solder mask and etch trapezoid.
- Confirm width against your fabricator’s stackup and impedance coupon.
Next step
- Change the stackup in the single-ended calculator — height, εr and copper change the result more than rounding does.
- Differential pairs — this page is single-ended only; numeric differential results are switched off, the page lists what to bring to a field solver.
For 50Ω stripline on FR-4 with 0.4mm plane spacing:
Assumptions: εr = 4.5, copper thickness = 0.035mm, plane spacing = 0.4mm. Stripline approximation: Z0 = 60/√εr · ln[4b/(0.67π(0.8w + t))], with validity w/(b−t) < 0.35. These are approximations; fabricators' field-solver results govern the final stackup.
Impedance Parameters
MOD: IMP_CAL_V1Differential impedance results are temporarily unavailable. The previous differential model was not validated against a field solver or a published source, so it has been switched off until it is. Single-ended Z0 below is for an isolated line and is not a differential result.
Embedded microstrip results are temporarily unavailable while the model is researched and validated.
b is the total plane-to-plane spacing. The approximation requires w/(b-t) < 0.35 and t/b < 0.25; both limits are exclusive.
Width Design
For 50Ω stripline
Single-ended Z0 (isolated line): 50.0 Ω
Impedance Control Tips
To Increase Impedance
- • Reduce trace width
- • Review laminate dielectric constant
To Decrease Impedance
- • Increase trace width
- • Reduce dielectric height
- • Review laminate dielectric constant
Understanding 50Ω Stripline Impedance
50Ω is a common single-ended target for RF circuits. This isolated-line calculation does not establish differential-pair impedance. To achieve 50Ω characteristic impedance using a stripline trace on standard FR-4 material (Er=4.5) with 0.4mm plane spacing, you need a trace width of approximately 0.1185mm (4.66 mil). This is an approximation based on IPC-2141-style and Hammerstad equations; confirm the final stackup with your fabricator's impedance report.
Key Parameters for 50Ω Design
- Target Impedance: 50Ω (characteristic impedance Z₀)
- Trace Type: Stripline (centered between two ground planes)
- Required Width: 0.1185mm (4.66 mil)
- Dielectric Constant: 4.5 (FR-4 standard)
- Plane Spacing: 0.4mm (layer spacing)
- Copper Thickness: 35µm (1oz copper)
- Effective Er: 4.500
- Propagation Delay: 7.076 ps/mm
Stripline vs Microstrip for 50Ω
Stripline traces are embedded between two reference planes, which gives shielding and a uniform dielectric (effective Er equals the material Er). For a given width, the achievable impedance range depends strongly on the plane spacing.
Common 50Ω Applications
50Ω impedance is required by the following standards and interfaces:
50Ω Standard Applications
IPC-2141 Impedance Formula
For stripline, the impedance calculation is simpler as the trace is fully embedded in the dielectric. The formula uses: Z₀ = (60/√Er) × ln(4b / (0.67π(0.8W + T))) where b is the total dielectric thickness and W is the trace width.
Frequently Asked Questions
How tight should my 50Ω trace width tolerance be?
The tolerance comes from your interface specification and your fabricator's process capability. As an illustration, a ±10% tolerance on a 50Ω target would be 45Ω to 55Ω. Specify controlled impedance to your PCB manufacturer and ask what width tolerance they hold.
Does copper thickness affect 50Ω impedance?
Yes, thicker copper slightly lowers impedance due to increased effective trace width. For precision designs, always include copper thickness in your impedance calculations. Our calculator uses35µm (1oz) as the standard.
What if my PCB uses different dielectric than FR-4?
High-speed designs often use low-loss materials like Rogers 4350B (Er=3.48) or Megtron 6 (Er=3.4). Lower Er requires wider traces for the same impedance. Use our full calculator above to input your specific material properties.
Related Impedance Calculations
Complete Your PCB Design
After calculating 50Ω stripline trace width, use our other free tools to complete your high-speed PCB design. Calculate trace current capacity and via sizing for your power delivery network.