USPS Media Mail rates*:
  Effective Jan 17, 2016
*note: these have NOT changed since May 2015

Up to 1 pound.......................................$2.72
More than 1 pound, less than 2 pounds....... 3.22
More than 2 pounds, less than 3 pounds.....3.72
More than 3 pounds, less than 4 pounds..... 4.22
More than 4 pounds, less than 5 pounds.....4.72
More than 5 pounds, less than 6 pounds.....5.22
More than 6 pounds, less than 7 pounds.....5.72
More than 7 pounds, less than 8 pounds.....6.22
More than 8 pounds, less than 9 pounds..... 6.72
More than 9 pounds, less than 10 pounds....7.22

Rates in blue are the most common postage rates for single-book shipments.

See the complete USPS list of prices here.

USPS First-Class Parcel rates:
Effective Jan 17, 2016
rates in red are less expensive than 1-lb Media Mail rate
Note USPS discount for printing First Class postage!

Between 3 and 4 ounces..............................2.74...$2.60 with Printable Postage
-----at this weight it becomes less expensive to use Media Mail rate if you are NOT printing with PBS Postage-----
Between 4 and 5 ounces..............................2.94.. $2.60 with Printable Postage
Between 5 and 6 ounces............................3.14 .. $2.60 with Printable Postage
Between 6 and 7 ounces.............................3.34....$2.60 with Printable Postage
Between 7 and 8 ounces............................3.54...$2.60 with Printable Postage

------------at this weight it becomes less expensive to use Media Mail rate------
  Between 8 and 9 ounces...........................3.74...$3.30 with Printable Postage
Between 9 and 10 ounces...........................3.92...$3.35 with Printable Postage
Between 10 and 11 ounces.........................4.14...$3.40 with Printable Postage
Between 11 and 12 ounces..........................4.34...$3.45 with Printable Postage
Between 12 and 13  ounces..........................4.54...$3.50 with Printable Postage
Between 13 and 14  ounces...................Priority Mail...$3.55 with Printable Postage
Between 14 and 15  ounces..........................Priority Mail ...$3.60 with Printable Postage
Between 15 and 15.999  ounces....................Priority Mail ...$3.65 with Printable Postage

[First Class Parcel rate does not exist above 13 ounces unless PBS Printable Postage is used]

See the complete USPS list of prices here.

If your package weighs 4 ounces or less and you are NOT using Printable Postage, First-Class rate will be about the same cost or less expensive than Media Mail rate, so First Class Postage will print out by default for packages up to 4 ounces being sent without Printable Postage.  If you use Printable Postage, the "cutoff" is 8 ounces - so **if you use Printable Postage and your (wrapped) package weighs up to 8 ounces, First Class Postage will print out by default on the PBS wrapper.

Please Note: Postage for First Class and Media Mail rate is determined by package weight.  MediaMail and First Class postal rates do not depend on distance--it will cost the same to send a package to any address served by USPS* (including AK, HI, PR, GU, US Virgin Islands and APO/FPO/DPO addresses) using either First Class or Media Mail.

*There is an exception for members who live in the Federated States of Micronesia - those members will NOT be able to use Media Mail to mail OUT books.  They will be able to accept books mailed with Media Mail rate.  Media Mail cannot be used to mail FROM the FSM, but it can be used to mail TO the FSM.

Related Links:

Can I use First-Class 'Large Envelope' Rate to send my book?
How much does it cost to mail a book?
Do I have to mail from a post office?
What materials can be sent by Media Mail postal rate?
Does the postage print out on the wrapper?
Is the postage amount shown on the PBS wrapper always correct?