Definition — What is an Uptime? 

In the world of computer technology, Uptime is the time that a website or web service is available to its users over a given period. It’s a measure of system or service reliability and stability. If a system or a service uptime is high, that means the system or the service is more reliable and stable. The term uptime is used in different computing elements which includes:

• Networks - It refers to the period the network is fully operational.
  

• CPU - It means how long the processor has been functioning since it was started.

• Servers - It's the duration that the server is operational and functional.
  

Although 100% uptime is the goal, the industry considers 99.999% uptime as high availability due to practical difficulties like downtime. At its most basic, a system’s uptime is simply the total time minus the downtime, but most monitoring services provide this information as a percentage. The formula for calculating the uptime percentage is the simple ratio of uptime divided by the total time.

99.9% uptime means your website may be down for a total of eight hours, 45 minutes, and 57 seconds each year.

99.99% uptime means your website may be down for a total of 52 minutes and 35.7 seconds each year.

99.999% uptime means your website may be down for a total of five minutes and 15.6 seconds each year.

99.9999% uptime means your website may be down for a total of 31.56 seconds per year.