Service Time Estimate Calculator

Work out service time estimate instantly with clear inputs, formula shown and shareable results.

About Service Time Estimate Calculator

Average service time alone is not enough for capacity planning, because it is the variability that creates queues. Separating fixed setup from the variable component shows where time can be removed, and the 90th percentile is what determines the worst-case customer experience.

Formulas

Average service time

Average = Total service minutes / Customers served

90th percentile

P90 = Average + 1.2816 x Standard deviation

Worked example

With the default values below, Service Time Estimate Calculator returns Average service time of 3.500. Change any input above and every figure here is recalculated in your browser.

Inputs used

Total service minutes recorded: 840
Customers served: 240
Fixed setup or greeting time per customer: 0.8
Coefficient of variation of service time: 0.6

Results

Average service time: 3.500
90th percentile service time: 6.19
Variable component per customer: 2.700
Standard deviation: 2.100

Step by step

1Values used
2Average service time
390th percentile
4Average service time= 3.500
590th percentile service time= 6.19
6Variable component per customer= 2.700
7Standard deviation= 2.100

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 3 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 does variability matter more than the mean?

Because queues form from the interaction of random arrivals and variable service. Halving variability reduces waiting more than shaving the mean by the same proportion.

How do I reduce service time?

Remove the fixed component first — pre-authorisation, pre-packing, self-service check-in — since it applies to every customer regardless of complexity.