Convert uptime percentages to actual downtime. Understand what SLA guarantees like 99.9% or 99.99% really mean for your services.
| SLA Level | Uptime % | Downtime/Year | Downtime/Month | Downtime/Week |
|---|---|---|---|---|
| Two Nines | 99% | 3.65 days | 7.31 hours | 1.68 hours |
| Three Nines | 99.9% | 8.76 hours | 43.83 min | 10.08 min |
| Four Nines | 99.99% | 52.6 min | 4.38 min | 1.01 min |
| Five Nines | 99.999% | 5.26 min | 26.3 sec | 6.05 sec |
| Six Nines | 99.9999% | 31.56 sec | 2.63 sec | 0.6 sec |
Uptime is the percentage of time a system, service, or website is operational and accessible. It's a critical metric for any online service because downtime directly impacts user experience, revenue, and trust.
Service Level Agreements (SLAs) typically guarantee a certain uptime percentage. Understanding what these percentages mean in real terms helps you set realistic expectations and choose appropriate service providers.
In the industry, uptime is often referred to by the number of nines in the percentage:
Each additional nine reduces allowed downtime by a factor of 10, but also typically requires significantly more infrastructure investment and operational complexity.
The formula for calculating uptime percentage is:
Uptime % = ((Total Time - Downtime) / Total Time) × 100
For example, if your service was down for 1 hour in a month (720 hours):
Uptime = ((720 - 1) / 720) × 100 = 99.86%
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