Three Nines SLA
99.9% Uptime Calculator

"Three nines" refers to 99.9% availability - the percentage contains three 9 digits. It is one of the most common SLA tiers offered for production web hosting and cloud services.

99.9% SLA allows about 8 hours, 45 minutes, and 36 seconds of downtime per year (using a 365-day year), roughly 43 minutes and 12 seconds per month.

For most business websites and internal applications, 99.9% is considered solid, industry-standard availability. High-traffic e-commerce, payments, or real-time systems often push for 99.99% or higher, since even a single multi-hour outage can consume most of a three-nines annual budget.

Four nines (99.99%) allows roughly 10 times less downtime than three nines (99.9%) - about 52 minutes per year instead of about 8 hours 45 minutes. Achieving that extra nine typically requires redundant infrastructure across multiple availability zones or regions.

99.9% is a common baseline SLA tier for single-instance compute, storage, and managed database offerings across major cloud providers. Multi-zone or multi-region deployments of the same services are typically what unlock the higher 99.95%-99.99% SLA tiers.