FR4 Trace Width Calculator
Standard FR4 | High-Tg FR4 | Halogen-Free FR4
Calculate trace width and impedance for FR4 PCB designs. FR4 is a common glass-epoxy PCB laminate family. Use supplier data for your selected laminate and verify the finished stackup with your fabricator.
FR4 Material Properties
| Property | Value or Data Source | Notes |
|---|---|---|
| Dielectric Constant (Dk) | 4.2-4.5 | typical, varies by laminate, frequency and resin content |
| Loss Tangent (Df) | See your laminate supplier datasheet | Check the operating frequency and test method |
| Glass Transition (Tg) | See your laminate supplier datasheet | Grade-specific |
| Breakdown Voltage | See your laminate supplier datasheet | Check test conditions and insulation requirements |
When to Use FR4
Ideal For
- • Digital designs with a verified signal-loss budget
- • USB 2.0, SATA, Gigabit Ethernet
- • Most microcontroller applications
- • Cost-sensitive designs
- • Consumer electronics
- • Industrial controls
Consider Alternatives For
- • High-speed signals with demanding loss budgets
- • PCIe 4.0+ interfaces
- • Long trace runs at high speed
- • RF/microwave applications
- • Low-loss requirements
- • Ultra-tight impedance tolerance
FR4 Design Guidelines
Dk Variation
FR4 Dk: 4.2-4.5 (typical, varies by laminate, frequency and resin content). Use your laminate supplier datasheet and fabricator stackup for design inputs.
Loss at High Frequency
FR4 loss depends on the laminate and frequency. For long high-speed traces, evaluate insertion loss against the signal margin required by your design.
Tg Selection
Choose Tg based on assembly and operating requirements. See your laminate supplier datasheet and confirm suitability with your fabricator.
Common FR4 Grades
Standard FR4
High-Tg FR4
Low-Loss FR4
Calculate FR4 Trace Dimensions
Use our free calculators for preliminary trace dimensions. For impedance inputs, see your laminate supplier datasheet and confirm the stackup with your manufacturer.
FR4 FAQ
What Dk should I use for FR4?
FR4 Dk: 4.2-4.5 (typical, varies by laminate, frequency and resin content). See your laminate supplier datasheet and confirm the finished stackup with your fabricator.
Is FR4 good for high-speed designs?
Suitability depends on the laminate, trace length, frequency, and signal-loss budget. Evaluate insertion loss and impedance with the actual stackup; consider low-loss materials where needed.
What's the difference between Tg levels?
Tg differs between laminate grades. See your laminate supplier datasheet and select a grade that meets the assembly and operating requirements with your fabricator.
Can I use FR4 for RF designs?
FR4 may suit some RF designs, depending on frequency, geometry, and the loss budget. Evaluate the actual laminate data and consider an RF laminate when tighter loss or impedance control is needed.
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