{"head":{"title":"What Is Uptime? Definition and the Nines Explained","description":"Uptime is the share of time a service is working and reachable, often written as a percentage like 99.9%. What each nine allows in downtime, plus mistakes.","canonical":"https://oceanlab.in/glossary/uptime"},"crumbs":[{"name":"Home","path":"/"},{"name":"Glossary","path":"/glossary"},{"name":"uptime","path":"/glossary/uptime"}],"slug":"uptime","term":"Uptime","aka":["availability"],"category":"Reliability","short":"The share of time a service is working and reachable, usually written as a percentage such as 99.9%.","body":[["Uptime is measured over a period, often a month. Each extra nine cuts the allowed downtime by ten. Over a 30-day month, 99% allows about 7.2 hours down, 99.9% about 43 minutes, and 99.99% about 4.3 minutes."],["How it is measured matters as much as the number. A service can respond to a health check and still fail for users. Better measures count successful user requests, which is what an ",{"href":"/glossary/slo","text":"SLO"}," does."]],"why":["Uptime is what users feel. It is also what an ",{"href":"/glossary/sla","text":"SLA"}," promises, so it drives how much to spend on redundancy, monitoring and on-call. Each extra nine costs more than the last, so the right target depends on what downtime costs the business."],"example":["An internal admin tool used in office hours is fine at 99.5%. A payments API used around the clock targets 99.95%, which needs multiple zones, automatic failover and deploys that can roll back in seconds."],"inBuild":["OceanLab publishes 99.9% uptime on its homepage. Reaching a target like that in a product build comes from the hosting set-up, monitoring, rollback and recovery plans decided before launch."],"mistakes":[["Promising four nines on infrastructure that has a single database."],["Not counting planned maintenance, which users experience as downtime anyway."],["Forgetting dependencies: your uptime cannot beat the services you rely on without fallbacks."]],"related":[{"href":"/glossary/sla","label":"SLA (service level agreement)","detail":"A contract that promises a level of service, such as uptime or support response time, and says what happens if it is missed."},{"href":"/glossary/slo","label":"SLO (service level objective)","detail":"An internal reliability target for a service, such as 99.9% of requests succeeding, measured by a service level indicator (SLI)."},{"href":"/glossary/rto","label":"RTO (recovery time objective)","detail":"How long a system can stay down after a failure before the outage seriously harms the business."},{"href":"/glossary/rpo","label":"RPO (recovery point objective)","detail":"The point in time to which data must be recoverable after an outage: in practice, how much recent data you can afford to lose."}],"tools":[],"links":[{"href":"/software","label":"Software by industry","detail":"Systems we build per industry, with guides and tools."},{"href":"/case-studies","label":"Case studies","detail":"Product builds by OceanLab, by industry."}],"sources":[],"legal":false,"updatedAt":"2026-10-25"}