How to know how many readers follow a blog?
I would like to contact bloggers and am interested to know how many readers they have.
Sometimes I can see a count (like a Feedburner icon with the number of readers). But most times I cannot see on the blog the number of readers...
How can I find out, or at least estimate?
You can add the blog's RSS feed to your Google Reader, and if you look at the details, it will show you how many people subscribe to that feed. You can also look at the Alexa ranking which would give you a rough idea of the number of visitors to the site (look at both the 3 month and 1 month to determine if the site is increasing, decreasing, or stable in terms of its ranking).
You can use feedburner to see how many people follow you. Wordpress also lets you see how many visitors your get and you can attempt to extrapolate from there