Calculator Inputs
Example Data Table
| Case | Width mm | Height mm | Length mm | Er | Frequency GHz | Z0 Ω | Inductance nH |
|---|---|---|---|---|---|---|---|
| FR-4 control trace | 1.20 | 0.80 | 50.00 | 4.30 | 2.40 | 56.31 | 16.841 |
| Thin substrate trace | 0.55 | 0.35 | 35.00 | 3.70 | 5.80 | 58.44 | 11.464 |
| Wide low impedance trace | 2.40 | 0.80 | 75.00 | 4.20 | 1.00 | 37.50 | 17.111 |
Formula Used
Width ratio: u = W_eff / h
Effective dielectric constant: for u ≤ 1,
εeff = (εr + 1) / 2 + (εr - 1) / 2 × [1 / √(1 + 12 / u) + 0.04(1 - u)²].
For u > 1, the final correction term is removed.
Impedance: for u ≤ 1,
Z0 = 60 / √εeff × ln(8 / u + 0.25u).
For wider traces,
Z0 = 120π / [√εeff × (u + 1.393 + 0.667ln(u + 1.444))].
Characteristic inductance:
L' = Z0√εeff / c. Total inductance is L = L' × length.
Capacitance and delay:
C' = √εeff / (Z0c), and delay = length × √εeff / c.
How to Use This Calculator
- Select millimeter or mil for trace geometry.
- Enter trace width, substrate height, and trace length.
- Add dielectric constant, conductor thickness, and frequency.
- Enter optional board count and review cost values.
- Press Calculate Now to show the result below the header.
- Use CSV or PDF buttons to save the calculated report.
Microstrip Inductance Planning Guide
Why geometry matters
A microstrip trace is more than a copper line. It is a controlled transmission path above a reference plane. Width, height, length, copper thickness, and dielectric constant shape impedance. They also shape inductance and signal delay. Small geometry changes can move a design away from its target. That can create extra prototypes, late board changes, and avoidable review costs.
Using inductance in project reviews
Characteristic inductance helps teams compare layout options quickly. A longer trace has more total inductance. A higher impedance line usually has higher inductance per length. This calculator converts geometry into usable values. It also reports capacitance, velocity, delay, and electrical length. These outputs support design checks, cost reviews, release decisions, and supplier discussions.
Interpreting the result
Start with impedance. Many RF and high speed layouts target 50 ohms, but your goal may differ. Then review inductance per millimeter. Use total inductance when the full routed length is known. Delay helps compare timing impact. Electrical length shows whether the trace becomes important at the selected frequency. A short trace at low frequency may be harmless. The same trace can matter at microwave speeds.
Budget impact
The budget section is optional. It estimates exposure from boards, review time, and a simple risk reserve. The reserve rises when impedance moves far from 50 ohms. This does not replace engineering judgment. It gives managers a clear way to compare layout risk with production cost. It also supports early decisions before ordering a prototype panel.
Good input practice
Use values from your stackup drawing. Check dielectric constant at the intended frequency. Confirm copper thickness after plating, because finished copper may differ from starting foil. Measure actual trace length from the routed path, not only the schematic net. Include bends and meanders when they add meaningful distance. For final work, compare this estimate with a field solver or manufacturer stackup tool.
Export and compare
Keep inputs consistent. Millimeters and mils are both supported, but mixing units creates bad results. Review the graph after each run. Wider traces usually reduce impedance and total inductance. Narrow traces usually raise both values. Export the PDF for approvals. Export the CSV when you need records for audits, budgets, or design notes. Save assumptions with every exported report for cleaner future review work.
FAQs
What is microstrip characteristic inductance?
It is the inductance per unit length implied by a microstrip line impedance and propagation speed. The calculator also multiplies it by trace length to estimate total inductance.
Is this the same as loop inductance?
No. This estimates transmission line characteristic inductance. Loop inductance depends on return current shape, plane gaps, vias, connectors, and nearby conductors.
Why is dielectric constant required?
Dielectric constant changes effective permittivity. That changes impedance, velocity, delay, capacitance, and inductance. Use the value from your board stackup.
Does copper thickness affect the result?
Yes. A simple effective width correction is applied. It improves estimates for common board copper, but exact values still need solver validation.
Can I use mil instead of millimeters?
Yes. Choose mil in the unit field. Width, substrate height, and trace length will be converted internally before calculation.
Why does the graph sweep trace width?
The graph shows how width changes impedance and total inductance. It helps you see whether widening or narrowing the trace improves the target.
What does budget exposure mean?
It combines board quantity, board cost, review hours, hourly rate, and a small reserve. It is a planning estimate, not an accounting record.
Should I use this for final RF signoff?
Use it for planning and early checks. For final signoff, confirm the design with stackup data, fabrication tolerances, and a field solver.