There are 4 different levels of certification determined by the Uptime Institute, which are internationally valid and focus on the capacity, redundancy and fault tolerance of a data center or IT infrastructure facility. In order to obtain Tier certificates, the technical requirements of each level must be fulfilled.
Uptime Institute TIER Comparison Table
| Tier I | Tier II | Tier III | Tier IV | |
| Building Type | Dependant | Dependant | Independant | Independant |
| Support Shift | None | 1 | More than 1 | 24 hour support |
| Standard Energy Per Cabinet | < 1 kW | 1-2 kW | 1-2 kW | 1-3 kW |
| Maximum Energy per Cabinet | < 1 kW | 1-2 kW | > 3 kW | > 4 kW |
| Raised Floor Height | 12” | 18” | 30-36” | 30-42” |
| Capacity of Components Supporting the IT Load | N | N + 1 | N + 1 | N + any fault |
| Redundancy | None | Yes | Yes | Yes |
| Power Distribution Channels | 1 | 1 | 1 active, 1 alternative | 2 simultaneously active |
| Concurrent Maintenance | No | No | Yes | Yes |
| Max. Permitted Outage Time | 28,8 hour | 22 hour | 1,6 hour | 0,8 hour |
| Uptime | % 99,67 | % 99,75 | % 99,98 | % 99,99 |