Server Uptime Calculator – Availability Percentage
Calculate server availability percentage from downtime duration.
About This Calculator
Calculate server availability percentage from downtime duration. Use the calculator above for instant results.
Worked Examples
- Uptime: 99.909% (3 nines nearly) | 8.76hr/yr allowed for 99.9%
Answer: 99.909% uptime
- Uptime: 99.4% | Just 2 nines
Answer: 99.4% uptime
- Uptime: 99.99% | 4 nines achieved!
Answer: 99.99% — 4 nines
Who Uses This Calculator?
Calculate and target availability percentages.
Set SLA targets.
Report on system reliability.
Design for target availability.
Common Mistakes to Avoid
❌ Nines sound better than hours
99.9% (3 nines) sounds great but is 8.76 hours of downtime per year. Know what your availability % means in real hours.
❌ Dependencies reduce availability
Three 99.9% components in series = 99.7% combined. Plan for cascading failures.
Frequently Asked Questions
SLA by number of nines?
99% = 87.6 hrs/yr. 99.9% = 8.76 hrs. 99.99% = 52.6 min. 99.999% = 5.26 min. 99.9999% = 31.5 sec.
How to achieve 4 nines?
Redundancy, failover, blue-green deployments, chaos engineering, automated recovery. Very expensive and operationally complex.
Cloud provider SLAs?
AWS EC2: 99.99%. Azure VMs: 99.99% (with Availability Zones). Google Compute: 99.99%. But SLA ≠ actual historical uptime.