Availability From Error Rate Calculator

Work out availability from error rate instantly with clear inputs, formula shown and shareable results.

About Availability From Error Rate Calculator

Request-based availability is successful requests over total requests, which reflects what users experienced far better than counting minutes the service was down. Converting the error ratio into equivalent full-outage minutes makes it comparable with a time-based SLA, and the nines figure is just the negative base-ten logarithm of the error rate.

Formula

Request availability

availability = 1 - failed / total; equivalent downtime = error rate x period minutes; nines = -log10(error rate)

Worked example

With the default values below, Availability From Error Rate Calculator returns Request-based availability of 99.95595%. Change any input above and every figure here is recalculated in your browser.

Inputs used

Requests in the periodminimum 1: 42,000,000
Failed requestsminimum 0: 18,500
Period lengthminimum 1 days: 30 days

Results

Request-based availability: 99.95595%
Error rate: 0.04405%
Equivalent full-outage minutes: 19.0 min
Nines achieved: 3.36

Step by step

1Values used
2Request availability
3Request-based availability= 99.95595
4Error rate= 0.04405
5Equivalent full-outage minutes= 19.0 min
6Nines achieved= 3.36

Assumptions and limits

The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax or fees or charges into account.
Figures are rounded for display to 5 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

Which is better, time-based or request-based availability?

Request-based, for user-facing services. A 30-second outage during peak traffic harms far more users than an hour at 3 am, and time-based measurement treats them as opposite.

What counts as a failed request?

Define it as part of the SLI: usually 5xx responses and timeouts, excluding client errors. Whether to count slow-but-successful responses is a separate latency SLI.