The nines, explained
99% allows more than three and a half days of downtime per year. 99.9% allows about eight hours and 45 minutes. 99.99% allows under an hour. 99.999% allows about five minutes. Each extra nine costs roughly ten times more engineering effort.
Measure your real uptime
Guessing is not measuring. A free monitor gives you the actual uptime percentage for the last 30 days.