On Friday, Google Operating System noticed that Google Reader will tell you Google Reader subscriber numbers for a blog when you search to add a new feed. It didn’t take long for different folks to start collecting subscriber numbers for different blogs. I haven’t asked the Reader team about this, but it looks like this is just the counts for Google Reader subscribers. Before charging off to compute a bunch of stats, you should know a few things:

1. A blog can have multiple feeds, and you may want to add up the subscribers for the most important feeds.

For example, here are subscriber numbers for my blog:

I got that data by going to Google Reader, clicking on “Add subscription” and then searching for the string “mattcutts”. If you have a unique string in your domain name, that’s a good way to see the top feeds for your site.

I’ve used orange letters to highlight that I have a feed at FeedBurner, a MyBrand feed (served by FeedBurner, but with a CNAME from my domain so I control the feed with DNS), an Atom Feed, and an RSS feed. If you add all those up together, you get 9980 subscribers. So I’m 20 readers short of ten thousand Google Reader subscribers. By the way, I think that MyBrand is one of the least-used but greatest features from FeedBurner (which was acquired by Google earlier this year). With MyBrand, your feed is served by FeedBurner, but you keep the control of the feed url in case you decide to leave FeedBurner some day. The best write-up on MyBrand that I’ve seen is this tutorial by Danny Sullivan.

2. You may have more users than your top few feeds suggest.

Modern blogging software such as WordPress can generate lots of different feeds. For example, for any post on my blog, you can subscribe to a separate feed for the comments on that post. All those little feeds can add up, so you might have a lot more subscribers than even the top few feeds on your site suggest. Which leads me right to:

3. FeedBurner can aggregate all your different Google Reader subscribers into one number.

If you just want a nice summary number, or to see the breakdown of feed readers, I recommend FeedBurner. It’s free and gives you useful stats for any day you want. Here’s a recent Monday’s stats for my blog:

Of course, FeedBurner will only give you stats for your own site. That’s why everyone is having a good time looking at the Google Reader subscriber counts. Just remember that Google Reader subscriber stats will skew toward Google users. That’s probably why some Google-focused blogs do better in Google Reader’s stats when compared to some other metrics.

Just as an aside, how cool is it that on Firefox with the Google search box, if you start typing in math, the auto-suggest will give you the running answer as a suggestion — without even hitting return? Here’s what it looks like:

Nice.

Anyway, if you want to lift my Google Reader subscribers above 10,000, just add my RSS feed or my Atom feed. I’m in a multi-week blogging lull as I work on a non-webspam project at the Googleplex, but I’ll be blogging more in 3-4 weeks.