I've found it to be correct maybe 40% of the time or less.  Today I mailed a book that had a "suggested postage" of $1.81 and the mailer was marked First Class... the Media Mail postage was $1.93 but First Class rate would have been something like $2.40!!  (It was wrapped in the PBS wrapper only, so it wasn't packing weight!)   Is it just because of my zip code (which is actually new york state), or are the postage rates just a ballpark wild guess??

I can never remember exact amounts to correct the system, btw--I noticed that they like it if you do that, but since they also ask on the other end I am always careful to enter the actual postage when I receive books and hope others will do the same.  :)

patti

Just because the weights are listed does not mean that they are right.  It is each member's responsibility to check the weight of the books they send.  Postal scales are not very expensive - they are even sold in the PBS store.  The best way to make sure that you are not paying too much for postage is to get a scale and check each book before you ship it.

You must have a couple of your numbers mixed up because media mail is never less than $2.13, but anyhoo, they are estimates based on weight. Depending on your wrapping it can bump up over the next level. When I first joined, every book was right at the PO. When paid postage came about, less than 10% of the estimates were right for what I was mailing. For the last few weeks I have had a good run and not had any come up wrong until one yesterday and one today.

When I use a plastic wrap and brown paper, I bump the weight 3-5 oz, with a bubble mailer I do at least 5 oz.  

I send all of my books from the post office, so I don't pay too much attention to the estimated cost, but I have noticed that since the move to prepaid postage more of the estimates on my packages are off, in both directions.

Sometimes the weights are off on books. I always way them first just to make sure.  Usually they are very close but sometimes they are way off. 

It was definitely less than $2--maybe the postage clerk made an error?  It was a very lightweight book.  :)  At any rate, I have to go to the post office to send and receive all my american mail, so weighing things is not an issue they do it for me!  Just wondering if my experience is the norm.  I had one postage clerk who was trying to just go by the estimates, and I told him please DON'T because they aren't always right and I definitely don't want to send a book postage due!!

I have found that many of the weights that the system says a book weighs is not correct and have wondered why it has to put the weight in at all. For me, it would be better if the weight had to be put in manually by the member sending the book  since packaging also has to be considered,

I didn't realize that was why you're asked for the postage amount on a book you receive.  I don't usually fill in that information, but I will from now on, if it helps with the postage accuracy for all of us :)

I have found most of mine to be accurate - maybe one out of 15 are incorrect.  I do think you may be confused on your rates, though because the absolute cheapest media mail rate is $2.13.  For books under a pound (I think...or maybe 13 oz?) first class is cheaper.

Edited to add:  Also, the rates don't change based on zip code, they are flat rates.

I've found the rates to be wrong at least 90% of the time.  I weigh just the book and it's always over or under.  If it's close for first class I juggle the weight around in the system to get the proper mailer.  I've had 8+ ounce books (without wrapping) show as eligible for first class.

I've found the weights to be wrong most of the time.  Now I wrap in plastic, weigh, add .5 and plug in that weight to get what it will actually be.

Well, okay, I will say that perhaps the actual weight listed is wrong on many books - but often this does not change how much you'll pay for postage as the weight only fluctuates when you go up and down entire pounds.  The best thing you can do is buy yourself a cheap postage or kitchen scale and weigh it yourself.