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PCB Impedance Calculator
Calculate single-ended microstrip characteristic impedance, effective dielectric constant, and signal propagation delay from trace width, dielectric height, and copper weight.
🔒 This tool runs entirely in your browser. Your files are never uploaded to a server.
Characteristic Impedance (Z₀)
Effective Dielectric (εeff)
Propagation Delay (tpd)
How it works
- Select the PCB dielectric core or prepreg material (e.g., FR-4, Rogers RO4350B, Polyimide) or specify a custom εr value.
- Enter your PCB trace width (W) and dielectric thickness height above the ground plane (H) in mils or millimeters.
- Select the finished copper weight (1 oz, 0.5 oz, or 2 oz).
- The calculator computes characteristic impedance (Z₀), effective dielectric constant (εeff), and signal propagation delay (ps/inch).
The formula
Z₀ = (87 / √(εr + 1.41)) × ln[5.98H / (0.8W + T)]
tpd (ps/in) = 84.75 × √(εeff)
FAQ
Why is 50-Ohm controlled impedance standard in PCB design?
50 Ohms provides the best compromise between maximum RF power handling and minimum signal attenuation for coaxial cables and microstrip traces.
What is the IPC-2141 microstrip impedance formula?
The IPC-2141 equation approximates single-ended surface microstrip impedance as Z₀ = (87 / √(εr + 1.41)) × ln[5.98H / (0.8W + T)], where W is trace width, H is dielectric height, T is copper thickness, and εr is relative permittivity.
How does dielectric constant (Er) affect trace width?
Higher dielectric constants (εr) require narrower trace widths to achieve a given impedance, while lower dielectric materials (like Rogers PTFE laminates) allow wider traces for lower resistive losses.
What is propagation delay in PCB traces?
Propagation delay (tpd) is the time it takes for an electrical signal wavefront to travel along a unit length of trace (typically ~140 to 180 picoseconds per inch on FR-4).
How we compare
| Feature | Online Tool Store | EDA vendor tools | Textbook charts |
|---|---|---|---|
| Dual unit support (Mils and Millimeters) | ✓ | ✓ | ✗ |
| Propagation delay & phase velocity metrics | ✓ | Partial | ✗ |
| Pre-loaded high-frequency laminate library | ✓ | ✓ | ✗ |