UPTIME

Uptime is the percentage of time a site or service is reachable and functioning over a given period. It is the headline reliability metric in web hosting, usually expressed as a "number of nines": 99.9% uptime (three nines) allows roughly 8.7 hours of downtime per year, 99.99% (four nines) allows under an hour, and 99.999% (five nines) under six minutes. Most reputable hosts publish an uptime guarantee in their SLA, typically 99.9% on shared plans and 99.99% on managed or enterprise plans. Independent third-party monitors (UptimeRobot, StatusCake, Pingdom) measure it from outside, which is more useful than the host's own number.

How it works

Uptime is measured by polling a site from multiple external locations at regular intervals (often every minute) and recording the percentage of successful responses. Downtime can come from anywhere in the chain: origin server failure, DNS issues, CDN outages, network problems, or even certificate expiry.

Why it matters

Every minute of downtime costs revenue, search ranking, and trust. The host's SLA is the contractual floor; what actually matters is real measured uptime over months. For e-commerce, a five-nines target is justified; for a blog, three nines is usually enough.

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Frequently Asked Questions