System Uptime / Availability
Percentage of time a system or service is fully operational
What is System Uptime / Availability?
System uptime, or availability, is the percentage of time a system is working and available to users. It shows how reliable a service is.
Customers depend on services being available, so uptime is often a contractual commitment and a key measure of operational quality.
How this KPI is measured
- Function
- Product & Engineering
- Sub-function
- Infrastructure & Reliability
- Industry
- All Industries
- Type
- Lagging
- Impact
- Operational
- Unit
- %
- Measurement frequency
- Monthly
- Formula
- ((Total time − Downtime) / Total time) × 100
How to calculate it
Subtract downtime from total time, divide by total time, and multiply by 100.
For example, if a service was down for 2 hours in a 30-day month of 720 hours, availability is (720 - 2) / 720 x 100 = 99.72%.
Be clear about what counts as downtime, such as full outage or serious degradation, and whether planned maintenance is included. Small percentages matter: 99.9% allows about 43 minutes of downtime per month.
Where it is used
Meeting service commitments
Track agreed availability.
Guiding reliability investment
Target frequent failures.
Reporting to customers
Show reliability.
How to improve it
Tips and common mistakes
- Each extra nine is much harder and costlier to achieve.
- Measure what users experience, not just server status.
- Be clear about planned maintenance.
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