What is uptime?

Uptime is the share of a given period during which a website or service is available and working. It is usually written as a percentage, such as 99.9%, and measured over a month or a year.

How is uptime measured?

An external monitor requests a page at regular intervals, often every one to five minutes, and records whether the answer is correct. Uptime is the number of successful checks divided by all checks, or equivalently the period minus the downtime, divided by the period. Because checks are samples, an outage shorter than the interval can be missed.

What does an uptime percentage allow?

Each nine cuts the allowed downtime to a tenth. 99% allows about 3 days 15 hours a year, 99.9% allows about 8 hours 45 minutes and 99.99% allows about 53 minutes. The uptime and SLA calculator works out any figure, and the page on 99.9% uptime explains the most common one.

Why does uptime matter for client sites?

A client judges you on the outages they see. Measured uptime lets you report a number instead of an impression, and it shows when a host or a deploy is the weak point.

Where Datumboard fits

Datumboard puts the signals behind this in one dashboard for your client sites and side projects. It is in early access, and you can join the list below.