Uptime SLA calculator
Each extra nine divides your downtime budget by ten. Three nines is nine hours a year; five nines is five minutes.
%
Availability multiplies through a chain of dependencies.
Downtime per year
8:45:58
- Downtime per month
- 0:43:50
- Downtime per week
- 0:10:05
- Downtime per day
- 0:01:26
- Number of nines
- 3.000
- Availability of the whole chain
- 99.900 00 %
- Chain downtime per year
- 8:45:58
Show the working
- Availability target = 99.9
- Serial components = 1
- unavailable = (100 - 99.9) / 100 = 0.001
- Downtime per year = 0.001 * 31557600 = 31 557.6
- Downtime per month = 0.001 * 2629800 = 2629.8
- Downtime per week = 0.001 * 604800 = 604.8
- Downtime per day = 0.001 * 86400 = 86.4
- Availability of the whole chain = (99.9/100)^1 * 100 = 99.9
- Chain downtime per year = (1 - (99.9/100)^1) * 31557600 = 31 557.6
- Number of nines = 99.9 < 100 ? -log10(1 - 99.9/100) : 99 = 3
Values are shown to six significant figures here; the arithmetic itself runs on exact fractions and is only rounded where a number is printed.
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The formula
- downtime = (1 - availability) x period
- serial availability = product of the component availabilities
Three components at 99.9% each give 99.7% together — about 26 hours a year, not 9.
The year here is the Julian year of 365.25 days, so the figures match the usual published SLA tables.