Propagation Delay Calculator
Calculate signal propagation delay through transmission lines, PCB traces, or cables. Determine how long signals take to travel through conductors.
FR-4: ~4.5
Use dielectric constant OR velocity factor
How to Use This Calculator
- Enter the trace or cable length in millimeters.
- Enter either the dielectric constant (εr) OR the velocity factor (0-1).
- The calculator displays the propagation delay in nanoseconds, picoseconds, and seconds.
- Use this to understand signal timing, design high-speed circuits, or match trace delays.
Propagation Delay Formula
Propagation delay is calculated from length and signal velocity:
Velocity = c / √εr (from dielectric constant)
OR Velocity = c × Velocity Factor (from velocity factor)
Where c = speed of light (299,792,458 m/s). Example: 100mm trace on FR-4 (εr = 4.5): Velocity = c/√4.5 = 141,421,356 m/s. Delay = 0.1 / 141,421,356 = 707 ps = 0.707 ns.
Full Description
Propagation delay is the time it takes for a signal to travel from one point to another through a transmission line, PCB trace, or cable. It's a critical parameter in high-speed digital circuits, RF systems, and timing-sensitive applications. Understanding propagation delay helps you design circuits with proper timing, match signal paths, and ensure synchronization.
Signal velocity depends on the dielectric constant (εr) of the material surrounding the conductor. Higher dielectric constants slow down signals. For FR-4 PCBs (εr ≈ 4.5), signals travel at about 47% of the speed of light. For air (εr = 1), signals travel at the speed of light. Cables have velocity factors (typically 0.66-0.85) that account for the dielectric material.
This calculator helps you determine propagation delay. Enter trace/cable length and either dielectric constant or velocity factor, and it calculates the delay. Use it when designing high-speed circuits, matching trace lengths, understanding signal timing, or analyzing RF systems. Propagation delay is fundamental to signal integrity and timing in modern electronics.
Frequently Asked Questions
What is propagation delay?
Propagation delay is the time it takes for a signal to travel through a transmission line, PCB trace, or cable. It depends on the physical length and the velocity of propagation, which is determined by the dielectric constant of the material.
How is propagation delay calculated?
Delay = Length / Velocity. Velocity = Speed of Light / √εr (for dielectric) or Speed of Light × Velocity Factor (for cables). For FR-4 PCB (εr ≈ 4.5): Velocity ≈ 0.47 × Speed of Light, so delay ≈ 6.7 ps/mm.
What is velocity factor?
Velocity factor is the ratio of signal velocity to speed of light (0 to 1). For air: 1.0. For cables: 0.66 (coaxial), 0.85 (twisted pair). For PCBs: ~0.47 (FR-4). Lower velocity factor means slower propagation and longer delays.
Why is propagation delay important?
Propagation delay affects signal timing, skew, and synchronization in high-speed digital circuits. In parallel buses, mismatched delays cause timing issues. In RF circuits, delay affects phase relationships. For clock signals, delay must be matched across traces.