What 99.9% uptime really means
Uptime figures all start with 99, so they look the same. In minutes of downtime they are very different.
The numbers in plain time
| Uptime | Downtime in a month | Downtime in a year |
|---|---|---|
| 99% | About 7 hours 12 minutes | About 3 days 16 hours |
| 99.5% | About 3 hours 36 minutes | About 1 day 20 hours |
| 99.9% | About 43 minutes | About 8 hours 46 minutes |
| 99.99% | About 4 minutes | About 53 minutes |
How uptime is measured
A monitoring service checks your site at a fixed interval and counts how many checks passed. Uptime is the share of checks that passed.
The interval matters. A site that is checked every five minutes can be down for four minutes without a single failed check. A check every minute sees much shorter outages.
The location matters too. A check shows what was seen from one place. A problem that only affects visitors in another region may not show up.
What a host's guarantee is worth
A hosting plan that promises 99.9% is allowed about 43 minutes of downtime a month. If it does worse, the usual remedy is a partial credit that you have to ask for, and you can only ask if you have your own record of the outage.
See your own numbers
KeenCrow checks every minute from a single location in the United States and shows your uptime for the last 24 hours, 7 days and 30 days, with every incident and how long it lasted.