CORE METRICS

System Uptime

The percentage of time that a system is fully operational and available to users.

Uptime % = (Total Time - Downtime) / Total Time × 100

The percentage of time that a system is fully operational and available to users.

## The Nines * **99% (2 Nines)**: Down 3.65 days/year. (Okay for blogs). * **99.9% (3 Nines)**: Down 8.76 hours/year. (Standard for SaaS). * **99.99% (4 Nines)**: Down 52 minutes/year. (Enterprise grade). * **99.999% (5 Nines)**: Down 5 minutes/year. (Telco/Critical Infrastructure). Each additional "nine" is 10x harder to achieve. The cost of going from 99.9% to 99.99% is often not worth it for most applications.

ExSaaS Platform Availability Journey

"B2B SaaS improved from 99.8% to 99.95% uptime over 12 months. Key changes: Implemented database failover, added caching layer, and improved deployment process. Customer churn dropped from 12% to 6%."

Impact

Doubled ARR growth through improved trust and retention

Resolution

Multi-region architecture with automated failover

Why Uptime Matters

The primary measure of reliability.

Often expressed in "Nines" (e.g., 99.9%).

Common Pitfalls

Chasing 5 nines (99.999%) prematurely

Focus on 3-4 nines first. The cost of 5 nines is rarely justified for non-critical systems.

Measuring uptime only at the server level

Measure from the user's perspective. Use synthetic monitoring to test actual user flows, not just server pings.

Industry Benchmarks

Consumer Apps8.76 hours/year downtime

99.9% (3 nines)

SaaS Business Apps4.38 hours/year downtime

99.95% (3.5 nines)

Enterprise SaaS52 minutes/year downtime

99.99% (4 nines)

Critical Infrastructure5 minutes/year downtime

99.999% (5 nines)

Related Terms

Downtime SLA SLO

Frequently Asked Questions

What does 99.9% uptime mean in hours?

99.9% uptime allows for 8.76 hours of downtime per year (43.8 minutes per month). This is the standard for most SaaS applications.

How many nines do I really need?

For most SaaS: 99.9% (3 nines) is sufficient. For critical infrastructure: 99.99% (4 nines). Each additional nine costs exponentially more.

What is the difference between uptime and availability?

Uptime measures if the system is running. Availability measures if users can successfully use the system. A site can be "up" but unavailable due to errors or slowness.