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Critical Path Timing Calculator

Work out critical path timing instantly with clear inputs, formula shown and shareable results.

About Critical Path Timing Calculator

The critical path is the longest logic chain between registers: stages times delay per stage plus wire delay, then derated for process, voltage and temperature variation. On-chip variation derates of 5-10% are typical and are applied before the path is declared timing-clean.

Formula

Critical path

delay = stages x delay per stage + wire delay, x (1 + OCV derate)

Worked example

With the default values below, Critical Path Timing Calculator returns Critical path delay of 885.60. Change any input above and every figure here is recalculated in your browser.

Inputs used

Logic stages on the path
8 stages
Average delay per stage
85 ps
Total wire delay on the path
140 ps
Timing derate for variation
8 %

Results

Critical path delay
885.60 ps
Logic delay
680.00 ps
Delay before derating
820.00 ps
Frequency limit
1,129.2 MHz

Step by step

  1. 1Values used
  2. 2Critical path
  3. 3Critical path delay= 885.60 ps
  4. 4Logic delay= 680.00 ps
  5. 5Delay before derating= 820.00 ps
  6. 6Frequency limit= 1,129.2 MHz

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, fees or charges 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 derate at all?

Because a chip must work at every corner of process, voltage and temperature. Derating covers within-die variation that corner analysis alone misses.

How do I shorten a critical path?

Reduce logic depth by restructuring, retime by moving registers, upsize critical gates, or pipeline the path into two shorter ones.

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