Wire Delay (Elmore) Calculator
Work out wire delay (elmore) instantly with clear inputs, formula shown and shareable results.
About Wire Delay (Elmore) Calculator
The Elmore delay of a driven RC line is Rd(Cw + Cl) + Rw(Cw/2 + Cl). The factor of a half on wire capacitance reflects its distribution along the line. Multiplying by 0.69 (ln 2) converts the Elmore time constant to a 50% propagation delay.
Formula
Elmore delay
T = Rdriver(Cwire + Cload) + Rwire(Cwire/2 + Cload); t50 = 0.69 T
Worked example
With the default values below, Wire Delay (Elmore) Calculator returns Elmore delay of 104.70. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Driver output resistance
- 800 Ω
- Wire resistance
- 120 Ω
- Wire capacitance
- 95 fF
- Receiver load capacitance
- 25 fF
Results
- Elmore delay
- 104.70 ps
- 50% propagation delay
- 72.24 ps
- Driver-dominated component
- 96.00 ps
- Wire self-delay component
- 8.70 ps
Step by step
- 1Values used
- 2Elmore delay
- 3Elmore delay= 104.70 ps
- 450% propagation delay= 72.24 ps
- 5Driver-dominated component= 96.00 ps
- 6Wire self-delay component= 8.70 ps
Assumptions and limits
- The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax or compounding frequency into account.
- Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
Why is wire capacitance halved?
Charge nearest the driver sees less wire resistance than charge at the far end. Integrating along the line gives an average of half.
When does the wire dominate?
When wire resistance approaches driver resistance — typically for long thin wires on lower metal layers, which is why critical global nets are routed on thick upper metal.
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