Every delivery request requires a size be specified for each manifest item that is specified in an order. Postmates uses this information to determine which mode(s) of delivery (walker, scooter, car, etc.) are viable, to communicate with the courier on space expectations for his or her vehicle, and when deciding if and when an order can be batched and/or chained.
Here are some handy guidelines to help you make the right size selection for your item(s)/package(s):
Note that no single item can weigh more than 50 pounds (roughly 23 kilograms) to be eligible for delivery.