Microstrip Impedance Calculator
Z₀ of a surface microstrip from width, height and εr (IPC-2141A), plus effective dielectric constant and propagation delay.
The IPC-2141 formula is an approximation, typically within ±5 % for 0.1 < w/h < 2.0. For production controlled-impedance boards, confirm the stack-up with your fabricator's field solver — actual εr varies with resin content, frequency and glass weave. Common targets: 50 Ω single-ended, 90 Ω USB differential, 100 Ω Ethernet differential.
Microstrip Impedance Calculator computes the characteristic impedance Z₀ of an outer-layer trace over a ground plane — free, instant and private in your browser. RF and high-speed digital designers matching 50 Ω lines, USB/HDMI routing and antenna feeds use it to skip the datasheet algebra: type your numbers, read the answer with the substituted formula shown step by step, and share an exact permalink of the calculation.
About Microstrip Impedance Calculator
Microstrip Impedance Calculator computes the characteristic impedance Z₀ of an outer-layer trace over a ground plane using the standard engineering relation: Z₀ = 87/√(εr+1.41) · ln(5.98h/(0.8w+t)) (IPC-2141A surface microstrip). Worked live: a 0.3 mm trace over 0.2 mm of FR-4 (εr 4.3) lands near 50 Ω. The result recalculates on every keystroke, the worked-example panel shows your numbers substituted into the formula, and the Copy permalink button encodes the inputs in the URL so a colleague opens exactly your calculation. Everything runs client-side — nothing you type leaves your device.
How to use Microstrip Impedance Calculator
- 1Enter your values — the tool starts with realistic defaults for this exact use case, so the worked example is meaningful immediately.
- 2Read the live result and the worked-example panel, which substitutes your numbers into the formula step by step.
- 3Adjust any input to compare scenarios, then use Copy result or Copy permalink to share the calculation.
Why use Microstrip Impedance Calculator?
- ✓Implements the real formula — Z₀ = 87/√(εr+1.41) · ln(5.98h/(0.8w+t)) (IPC-2141A surface microstrip) — with the substitution shown, not a black box
- ✓Built for RF and high-speed digital designers matching 50 Ω lines, USB/HDMI routing and antenna feeds
- ✓Copy result and permalink buttons — share the exact calculation in a README, forum answer or design review
- ✓100% free, no sign-up, runs entirely in your browser (works offline once loaded)
Frequently asked questions
How do you calculate microstrip impedance?+
The characteristic impedance Z₀ of an outer-layer trace over a ground plane follows Z₀ = 87/√(εr+1.41) · ln(5.98h/(0.8w+t)) (IPC-2141A surface microstrip). For example, a 0.3 mm trace over 0.2 mm of FR-4 (εr 4.3) lands near 50 Ω. The calculator applies the same relation and shows the substituted arithmetic so you can verify every step.
How accurate is the IPC-2141A microstrip formula?+
Within a few percent inside its validity window (0.1 < w/h < 2, εr < 15). Solder mask, etch factor and glass-weave variation shift real boards a couple of ohms, so fabs verify controlled-impedance orders with a field solver and test coupons.
Why does my impedance come out too low?+
Usually the trace is too wide for the dielectric height. Z₀ falls as w/h grows — on thin 4-layer prepregs (~0.1 mm to L2) a 50 Ω line is only ~0.18 mm wide. Thicker dielectric or a narrower trace raises it.
Is the Microstrip Impedance Calculator free and private?+
Yes — completely free with no sign-up or usage limits, and it runs entirely in your browser: the values you enter are never uploaded or stored on a server.
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