Just Exactly What is a Unique Visitor?

What’s the difference between a unique visitor and a user? This post will outline the basics. Many people make the mistake of equating the two, and there are some substantial differences.

First let’s look at how a web analytics package measures a visitor. The first step is to cookie the machine when a user visits it. Once the cookie is set, that machine is considered a unique visitor.

Whether or not that person is considered a unique visitor the next time they visit a site depends on the time interval being measured. For example, let’s say you had 5,000 unique visitors on Monday, and 4,700 unique visitors on Tuesday. Wee some of Tuesday’s visitors may have visited the site on Monday too. So for Monday and Tuesday together, you may have had only 9,000 unique visitors (because 700 visited both days).

As I said before, a unique visitor does not equate to a unique visit by a human user. It equates to a unique visit by a machine that has not deleted it’s cookies. Here are the major differences:

  1. More than one human user may be using the same machine. A perfect example of this is a home machine shared by a family. In this case, many people will potentially seem like one unique visitor.
  2. A single human user may use more than one machine. Many people have computers at their office and a different one at home. In this case, a single user will seem like 2 unique visitors.
  3. If a user visits your web site, deletes their cookies, and then comes back, they will look like 2 unique visitors.

One method for getting better data is to require registration. In this event, each human user might have a different account, and more detailed tracking becomes significantly easier. This method is not perfect either, as there are people that share such accounts.

What’s important to remember in analytics is that perfect measurement is not possible. Your goal with an anlaytics tool needs to be to effectively measure trends and ways to increase business done through your site.

So if your analytics software says that your traffic went from 100,000 unique visitors last month to 150,000 this month, you know you have grown your traffic. While the real numbers might be 110,000 unique visitors last month and 160,000 this month, you can’t worry about that.

There is no way to get better precision, and you have to accept the limitations of the tools. They still provide an awesome resource for growing your business.


  1. says

    Very timely post Eric we were just discussing this at work. I think the numbers aren’t absolute but relative. This is much like the numbers you get on keywords, take them with a grain of salt. Now if I can only get 100,000 visits a month, then who cares if they’re unique.

  2. Bill says


    Do you have some sense on what impact a proxy server has on unique visitorship? We are noting that many large corporations are using proxy servers which are caching the pages for the company’s employees, effectively reducing unique visitorship.

    Any comments?


  3. Eric Enge says

    Hi Bill,

    This really should not reduce unique visitors, provided that your analytics software is using cookies to track visitors. Of course, if you are using a package that tracks by IP address, an proxy server can mess that up.


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