PCB Trace Signal Delay

td = length / vp

Quick answer

This calculator solves td = length / v_p for Signal Delay. With Trace Length 10 mm, Propagation Velocity 0.5, the result is 20 ms. It solves in 3 directions, so you can enter the values you have and get the one you need.

Calculator

Signal Delay (ns)
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Formula

td = length / v_p

Description

The signal delay through a PCB trace is simply the trace length divided by the propagation velocity. This is critical for high-speed digital design where signals on different nets must arrive at the receiver within a specified time window (setup and hold times). Length matching ensures that parallel data bus signals and their clock arrive simultaneously. For DDR memory interfaces, differential pairs, and LVDS links, delay matching to within 5-25 ps (1-5 mm) is commonly required.

Variables

  • td — Signal propagation delay (s)
  • length — Physical trace length (m)
  • v_p — Propagation velocity (m/s)

Practical Notes

For FR-4 microstrip, the delay is approximately 6.0-6.3 ps/mm (150-160 ps/inch). For FR-4 stripline, the delay is approximately 6.8-7.1 ps/mm (170-180 ps/inch). A 100 mm microstrip trace has about 600 ps delay. For a 1 GHz clock (1 ns period), this is 60% of one clock period, which is very significant. Trace delay must be accounted for in timing budgets for any interface faster than about 50 MHz.

Symbols and units

Symbol Meaning Default unit Accepted units
td Signal Delay ns ps, ns, µs, ms, s, min, h
length Trace Length mm mm, cm, m, km
vp Propagation Velocity — —

Step by step

  1. 1. What you know: Trace Length 10 mm, Propagation Velocity 0.5
  2. 2. The relation: td = length / v_p
  3. 3. Substitute: length = 10 mm, vp = 0.5
  4. 4. Result: Signal Delay = 20 ms

Worked examples

Minimum range

Given: Trace Length 0.1 mm, Propagation Velocity 0.025

Result: Signal Delay = 4 ms

Low range

Given: Trace Length 1 mm, Propagation Velocity 0.25

Result: Signal Delay = 4 ms

Typical

Given: Trace Length 10 mm, Propagation Velocity 0.5

Result: Signal Delay = 20 ms

High range

Given: Trace Length 10 cm, Propagation Velocity 0.8

Result: Signal Delay = 125 ms

Maximum range

Given: Trace Length 1 m, Propagation Velocity 8

Result: Signal Delay = 125 ms

Solving for each variable

Solve for Signal Delay

Trace Length 0.1 mm, Propagation Velocity 0.025 → 4 ms

Solve for Trace Length

Signal Delay 100 ps, Propagation Velocity 0.025 → 2.5 × 10⁻⁹ mm

Solve for Propagation Velocity

Signal Delay 100 ps, Trace Length 0.1 mm → 1 × 10⁶

How Signal Delay changes with Trace Length

Trace Length (input) Signal Delay (result)
1 mm 2 ms
2.5 mm 5 ms
5 mm 10 ms
7.5 mm 15 ms
10 mm 20 ms
15 mm 30 ms
2 cm 40 ms
4 cm 80 ms
7 cm 140 ms
10 cm 0.2 s

The same result in other units

Unit Value
µs 20000
ms 20
s 0.02
min 0.0003333

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Frequently asked questions

How do you calculate PCB Trace Signal Delay?

Use td = length / v_p. With Trace Length 10 mm, Propagation Velocity 0.5, Signal Delay works out to 20 ms.

How do you calculate delay 20ps in 100g pcb trace?

Rearrange for Signal Delay: with Trace Length 1 mm, Propagation Velocity 0.25, Signal Delay is 4 ms.

How do you calculate critical pcb signal length?

Rearrange for Signal Delay: with Trace Length 10 mm, Propagation Velocity 0.5, Signal Delay is 20 ms.

What is the formula for PCB Trace Signal Delay?

The formula is td = length / v_p. The signal delay through a PCB trace is simply the trace length divided by the propagation velocity.

How do you find Trace Length when you know the other values?

Rearrange for Trace Length: with Signal Delay 100 ps, Propagation Velocity 0.025, Trace Length is 2.5 × 10⁻⁹ mm.

How do you find Propagation Velocity when you know the other values?

Rearrange for Propagation Velocity: with Signal Delay 100 ps, Trace Length 0.1 mm, Propagation Velocity is 1 × 10⁶.

Related Concepts

All PCB & Traces formulas →
Trace Current Capacity (IPC-2221) Trace Resistance Trace Voltage Drop Via Current Capacity (IPC-2221) Microstrip Impedance Stripline Impedance Differential Pair Impedance Near-End Crosstalk

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