What is the KPI for uptime?
The main KPI for uptime is the uptime percentage: the share of time your site was available over a given period. It's calculated as:
uptime % = (available time / total time) × 100
Most websites target 99.9% uptime or higher. That sounds close to perfect, but the gap between "three nines" and "four nines" matters a lot:
| Uptime | Max downtime per month | Max downtime per year |
|---|---|---|
| 99% (two nines) | ~7.3 hours | ~3.65 days |
| 99.9% (three nines) | ~44 minutes | ~8.76 hours |
| 99.99% (four nines) | ~4.4 minutes | ~52 minutes |
| 99.999% (five nines) | ~26 seconds | ~5.3 minutes |
"Five nines" is the gold standard for critical infrastructure, but for most websites 99.9% is a healthy, achievable target.
To actually hit (and prove) any uptime KPI, you need continuous monitoring with reliable historical data. Oh Dear tracks this for every monitor you add and shows it on each uptime report so you can share real numbers with your team, customers, or auditors.
