one of the most importing criteria when choosing a web hosting is the service availability, it is calculated with ratio and generally it is about 99% and mor precisely between 99,0% to 99,9% for premium web hosting, lets take an example 000webhsot is a free web hosting that I use a lot and if you check their web site you will find that the available service is 99% but they mention that their servers reach generally 99,9% then when w check their premium hosting we read 99,9% of availability
but what does it mean 99% availability?
we know a month is 30 days and a day is 24 hours and an hour is 1440 minutes
99,0% availability means the server shouldn't go down for more than 14,4 minutes in a day or 7,2 hours per month
99,9% availability means the server shouldn't go down for more than 1,44 minutes in a day or 43,2 minutes per month
you see, at first glance it looks like 99,0% or 99,9% is not a big deal but when you see how much your server can go down (and that means no visitors, no emails no sales, no conversion) 432 minutes per month vs 43,2 minutes per month it is 388,8 minutes almost 6,48 hours between 99,0% and 99,9%
hope this article was useful for you