Amtrak's luggage rules are available at Amtrak.com. The website lists the acceptable dimensions for both checked and carry-on luggage, the number of bags allowed, information on restricted items and the policy for specialty items that might not fit the size requirements.
From any page of the Amtrak website, click on Baggage Info and Service under the Experience menu at the top of the page. Under each luggage description, click on the link to find more detailed information. Aside from the luggage policies, Amtrak offers tips for packing efficiently and details on services such as baggage assistance, liability, temporary storage and even shipping.