The meta description tag is an interesting one from an SEO standpoint. It is a very important tag given it's potential impact on clickthrough rates in the SERPs as well as it's (albeit limited and unclear) impact on your site's relevancy (and ranking) for targeted keywords. However, search engines choose whether or not to show what you include in the meta description tag, versus some another snippet it may deem better for the user. This fact can be frustrating at times, and we'll deal with it more in-depth in a later (and more advanced) post.
Today's post seeks to answer the question: "Now that I'm going to go through the trouble of creating quality meta descriptions, what should their target length and maximum length be?"
Again, the answer is not easy (at least not as easy as with the maximum length for title tags), but I'll go ahead and say that you should target 150 characters (which is also the maximum length that Google will show), and do your best to stay within 250 characters as a maximum (I've heard the 255 and 260 figures thrown around a lot). Google says publicly that there is no max length, but guidelines are always good to have and these are the ones I go by.