UPS is pretty strict on weight and packages with UPS can weigh up to 150 lbs without incurring additional fees.
Packages that weigh more than 150 lbs are considered freight.
Packages that are sent by regular UPS ground or air can be up to 108 inches long and 165 inches in length and girth combined.
UPS charges for shipping by both size and weight.
The dimensional weight is calculated based on the packages length, width and height and is used to account for large and lightweight packages.
UPS also uses the actual weight of the package and will also charge based on the higher of the actual weight or the dimensional weight.
UPS does mail small packages as I've both received small packages and have shipped small packages through UPS.
FedEx also ships small packages, although FedEx and UPS are both more expensive for shipping small packages than the USPS is.
USPS is cheaper than UPS for small packages and UPS is often cheaper than USPS for larger packages.
If your package is large or is over 70 lbs then you should ship it through UPS or even FedEx but if it's a small package then you should ship it through USPS ground advantage if it fits the requirements.
The best way to mail a small package is to mail the small package through USPS ground advantage which is the cheapest option.
FedEx and UPS cost more to ship small packages so the USPS is best for small packages.
For shipping costs the USPS is the cheapest, especially for shipments of small packages.
I've shipped a small package that costs $15.60 to ship at FedEx and the same size package and same weight package cost only $7.10 to ship with USPS using USPS ground advantage.
UPS is often more expensive to ship with than FedEx and USPS.
Small packages are often better shipped using USPS ground advantage and larger packages are better shipped through UPS or FedEx.