Service Level Agreement (SLA) and Number of 9s

To commit to memory, SLA 9s and acceptable unscheduled downtime:

Availability %	Approximate downtime/ year
90	50,000 minutes (800 hours)
99	5,000 minutes (80 hours)
99.9	500 minutes (8 hours)
99.99	50 minutes (1 hour)
99.999	5 minutes
99.9999	0.5 minutes

In more details, for reference:

Availability %	Downtime/ year	Downtime/ month*	Downtime/ week
90% (“one 9”)	36.5 days	72 hours	16.8 hours
95%	18.25 days	36 hours	8.4 hours
98%	7.30 days	14.4 hours	3.36 hours
99% (“two 9s”)	3.65 days	7.20 hours	1.68 hours
99.5%	1.83 days	3.60 hours	50.4 minutes
99.8%	17.52 hours	86.23 minutes	20.16 minutes
99.9% (“three 9s”)	8.76 hours	43.2 minutes	10.1 minutes
99.95%	4.38 hours	21.56 minutes	5.04 minutes
99.99% (“four 9s”)	52.56 minutes	4.32 minutes	1.01 minutes
99.999% (“five 9s”)	5.26 minutes	25.9 seconds	6.05 seconds
99.9999% (“six 9s”)	31.5 seconds	2.59 seconds	0.605 seconds

* Assume a 30-day month.