Impedance Calculator
Microstrip / Stripline / Differential Pair
Calculate characteristic impedance for high-speed PCB traces using our free online impedance calculator. Supports microstrip, stripline, and differential pair configurations for USB, HDMI, PCIe, DDR, and other high-speed interfaces.
Microstrip Impedance
Calculate microstrip impedance using Hammerstad-Jensen equations. Ideal for surface layer routing where traces run above a ground plane with controlled dielectric height.
Stripline Impedance
Calculate stripline impedance for traces sandwiched between two ground planes. Provides better EMI shielding and consistent impedance for sensitive high-speed signals.
Differential Pairs
Calculate differential pair impedance for USB, HDMI, LVDS, and other high-speed interfaces. Design 90Ω, 100Ω, or custom differential impedances with edge or broadside coupling.
Impedance Parameters
MOD: IMP_CAL_V1Impedance Check
Why Impedance Control Matters
Signal Integrity
Impedance mismatches cause signal reflections that degrade eye diagrams and increase bit error rates. Proper impedance control ensures clean signal transmission for high-speed digital interfaces.
EMI/EMC Compliance
Controlled characteristic impedance reduces electromagnetic emissions and improves immunity. Essential for meeting FCC, CE, and other regulatory requirements.
High-Speed Interface Support
USB 2.0/3.0 (90Ω), HDMI (100Ω), PCIe (85Ω), DDR4 (40-60Ω) all require precise impedance matching. Our calculator supports all common interface standards.
Stackup Optimization
Use our impedance calculator to optimize your PCB stackup before fabrication. Adjust trace width, dielectric thickness, or copper weight to achieve target impedance.
Design Mode
Specify your target impedance (50Ω, 100Ω, etc.) and automatically calculate the required trace width for your stackup parameters.
Multiple Dielectric Materials
Supports FR-4, Rogers, Isola, Megtron, and custom dielectric constants. Accurate impedance calculation for standard and high-frequency materials.
Impedance Calculator Technical Guide
Characteristic impedance (Z₀) is the ratio of voltage to current for an electromagnetic wave propagating along a transmission line. For PCB traces, this impedance depends on trace geometry, dielectric properties, and the relationship to reference planes.
Our microstrip impedance calculator uses the Hammerstad-Jensen equations, which are accurate within ±2% for typical PCB geometries. For stripline impedance, we use IPC-2141 formulas optimized for symmetric stripline configurations.
Differential pair impedance depends on both the single-ended impedance of each trace and the coupling between traces. Tighter coupling (smaller spacing) increases coupling factor and typically reduces differential impedance. Our calculator handles both edge-coupled and broadside-coupled configurations.
For production PCBs, always specify impedance control to your fabricator and expect ±10% tolerance for standard processes. Critical applications may require test coupons and TDR (Time Domain Reflectometry) verification to ensure impedance accuracy.
Common Impedance Targets
Related Tools
Impedance Control FAQ
What is characteristic impedance and why does it matter?
Characteristic impedance (Z₀) is the ratio of voltage to current for a wave traveling along a transmission line. For high-speed signals, impedance mismatches cause reflections that degrade signal integrity. Standard impedances are 50Ω for single-ended and 100Ω for differential signals in most applications.
When should I use microstrip vs stripline?
Microstrip (surface trace over ground plane) is easier to manufacture and preferred for most high-speed signals. Stripline (trace between two ground planes) provides better shielding and consistent impedance but is more expensive. Use stripline for sensitive signals requiring EMI protection or when routing through inner layers.
How accurate are these impedance calculations?
These formulas (Hammerstad-Jensen for microstrip, IPC-2141 for stripline) are accurate within ±5% for typical PCB geometries. For production, always specify impedance control to your fab house and expect ±10% tolerance. Critical applications may require test coupons and TDR verification.
What dielectric constant should I use for FR-4?
Standard FR-4 has Er = 4.2-4.8, typically 4.5 at 1MHz. For high-speed designs (>1GHz), use frequency-dependent values from your laminate datasheet. Low-loss materials like Rogers (Er ≈ 3.5) or Megtron (Er ≈ 3.4) are preferred for multi-gigabit signals.
How do I design differential pairs for 100Ω impedance?
Start with single-ended traces at ~50-55Ω, then adjust spacing for 100Ω differential. Tighter coupling (smaller spacing) increases coupling and reduces differential impedance. Common configurations: USB 3.0 (90Ω), HDMI (100Ω), PCIe (85Ω). Always verify with your fab's stackup.
Does trace thickness affect impedance?
Yes, thicker copper (higher oz weight) slightly reduces impedance due to the increased cross-sectional area. The effect is typically 1-3Ω for standard copper weights. Our calculator accounts for copper thickness in impedance calculations.
Related Articles & Guides
Microstrip vs Stripline vs CPW Guide
Compare microstrip, stripline, and coplanar waveguide for high-speed PCB design. Impedance calculations and use cases.
High-Speed Impedance: USB, HDMI, PCIe
Complete reference guide for high-speed interface impedance requirements. Covers USB 2.0/3.0, HDMI, PCIe Gen 1-5, DDR3/4/5, and more with practical design tips.
5 Free PCB Calculators for Engineers
Essential online calculators for PCB design: trace width, via current, impedance, and more. Boost your productivity with these free tools.
PCB Design Checklist: 25 Key Points
Never send a flawed PCB to manufacturing again. 25-point checklist covering trace widths to impedance matching.
Other PCB Calculators
Trace Width Calculator
Calculate PCB trace width for your current requirements using IPC-2221 standard. Free online tool for copper thickness, temperature rise, and voltage drop analysis.
Try Calculator →Via Current Calculator
Calculate via current carrying capacity based on IPC-2221 standard. Free tool for plated through-hole thermal analysis and via array design optimization.
Try Calculator →Related Tools & Resources
Trace Width Calculator
CalculatorCalculate PCB trace width for your current requirements using IPC-2221 standard. Free online tool for copper thickness, temperature rise, and voltage drop analysis.
Via Current Calculator
CalculatorCalculate via current carrying capacity based on IPC-2221 standard. Free tool for plated through-hole thermal analysis and via array design optimization.
Differential Impedance Calculator
CalculatorDesign differential pairs for USB, HDMI, PCIe, and other high-speed interfaces
Rogers Impedance Calculator
MaterialHigh-frequency RF calculations for Rogers materials
USB Trace Calculator
StandardUSB 2.0/3.0/4.0 differential pair design
HDMI Impedance Calculator
StandardHDMI 1.4/2.0/2.1 high-speed design
Complete Your PCB Design Analysis
Our impedance calculator is part of a comprehensive PCB design toolkit. Calculate trace widths for power delivery or analyze via current capacity for layer transitions.