Uptime/Availability Calculator (Nines)
Nines of Availability
Calculate allowed downtime from availability percentage
Composite Availability
Calculate combined availability of dependent components
Formula
Downtime/Year = 525,960 min x (1 - Availability/100) | Series = A1 x A2 x A3 | Parallel = 1 - (1-A1)(1-A2)(1-A3)
Frequently Asked Questions
What do the 'nines' mean?
The nines refer to the number of 9s in the availability percentage. Two nines (99%) = 3.65 days downtime/year. Three nines (99.9%) = 8.76 hours. Four nines (99.99%) = 52.6 minutes. Five nines (99.999%) = 5.26 minutes. Each additional nine represents a 10x reduction in allowed downtime.
How is composite availability calculated?
For series (dependent) components: multiply all availabilities (A1 x A2 x A3). For parallel (redundant) components: 1 - product of unavailabilities: 1 - (1-A1)(1-A2)(1-A3). Two 99% components in series = 98.01%. Two 99% components in parallel = 99.99%.
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