As a teacher I have heard many horror stories of art supply purchases gone bad.  If you have ever been to an art supply store you can see why, to a beginning artist, the choices are astounding.  If you are looking to buy paper you have an array  of choices, drawing paper, watercolor paper, charcoal paper, etc.  With watercolor papers alone there are so many varieties that are often categorized in lbs. (What does that mean?), textures, pads, blocks, and individual sheets.  Naturally, if you are taking an art class the best thing to do is to get a supply list from your instructor.  But there might be times when you just want to experiment but don't want to make an unnecessary expensive purchase.  Some of the Arts and Crafts chains (Michael's, for example) can be a convenient place to buy art supplies.  They usually offer good discounts but can be limiting to the professional artist.  Also, the salespeople there may or may not be experienced in offering advice in the fine arts.  We have a local art supply store, Blick, which is very good and its location near one of the best art schools in the country (Rhode Island School of Design) mostly assures that you will get top notch advice.  It also has an online store (www.dickblick.com).  Lately I have been ordering my art supplies online at  www.jerrysartarama.com.  The prices are very good and they also have chain stores that will match online prices.  One thing I like about the site is that it offers a great customer service and a "live chat".  Many websites offer a live chat which is a service where you type your questions to a real person and you can have a back-and-forth help session.  On JerrysArtarama website the live chat is located in the upper right corner of the Home page.  Ordering is very clear and easy and takes only a few days to arrive.  They also offer a guarantee.  Free shipping is offered for purchases over a certain amount.  If you are in a class your could do a group order to save on shipping.  However, we all know how quickly art supply purchases can add up, so you may not need a group order, lol.  

FYI - Watercolor paper is labeled in lbs. often 90 lbs. or 140 lbs.   This will be the weight for each ream (500 sheets) of that particular paper.  Therefore a paper with a weight of 140 lbs. will be thicker and thus heavier than one with a weight of 90 lbs.