What Is an SLA?
A Service Level Agreement (SLA) is a commitment from a service provider that defines the expected level of service, including uptime guarantees. When a provider promises "99.9% uptime," they're committing to a specific maximum amount of downtime over a given period.
The Nines Explained
The difference between each "nine" of availability is dramatic:
| SLA Level | Nickname | Downtime/Year | Downtime/Month |
|---|---|---|---|
| ----------- | ---------- | --------------- | ---------------- |
| 99% | Two nines | 3 days 15 hours | 7 hours 18 min |
| 99.9% | Three nines | 8 hours 45 min | 43 min 12 sec |
| 99.99% | Four nines | 52 min 33 sec | 4 min 19 sec |
| 99.999% | Five nines | 5 min 15 sec | 25.9 sec |
Why This Matters
The jump from 99.9% to 99.99% uptime might seem small — just 0.09% — but it represents nearly 8 fewer hours of allowed downtime per year. That's the difference between a service being down for an entire workday versus being down for less than an hour.
How to Calculate Allowed Downtime
The formula is simple:
Allowed downtime = Total time period x (1 - SLA percentage)
For example, for 99.9% uptime in a 30-day month:
- 30 days = 2,592,000 seconds
- Allowed downtime = 2,592,000 x 0.001 = 2,592 seconds = 43 minutes 12 seconds
Use our SLA Calculator to quickly convert any SLA percentage to allowed downtime.
Real-World SLA Examples
Most major cloud providers offer SLAs in the three to four nines range:
- AWS typically offers 99.99% for compute services
- Google Cloud offers 99.95% to 99.99% depending on the service
- Azure offers 99.9% to 99.99% for most services
You can monitor whether these providers are meeting their SLA commitments on our incidents page.
What Happens When an SLA Is Breached?
Most SLAs include service credits as compensation for downtime exceeding the guaranteed uptime. However, these credits rarely cover the full business impact of an outage. That's why proactive monitoring is essential — knowing about an outage before your users do gives you time to activate failover plans.
Monitoring Your SLAs
ServiceAlert.ai monitors 600+ cloud services in real time. Set up alerts to get notified the moment a service you depend on goes down, via email, Slack, Teams, Google Chat, or Discord.