What is a good uptime percentage for a website?

99.9% (three nines) is the industry standard for business websites — about 8.7 hours of downtime per year. Revenue-critical SaaS should target 99.95% (4.4 h/year); infrastructure providers commit to 99.99% (52 min/year).

• 99% uptime = 3.65 days of downtime per year — too much for a paying-customer product.
• 99.9% (three nines) = 8h 46m/year — the default SLA for most B2B SaaS.
• 99.99% (four nines) = 52m 36s/year — requires multi-region failover.
• 99.999% (five nines) = 5m 15s/year — telecom / core-infrastructure territory only.