Limitation on the number of pets for United Airlines (UA)

United Airlines imposes strict limits on the number of animals allowed in the lower deck cargo holds.
According to UA, the limits are:

For flights under 2 hours:
Extra Small = 15,
Small / Medium = 6,
Intermediate = 4,
Large = 3,
Extra Large = 2,
Giant = 1,

For flights over 2 hours:
Extra Small = 7
Small / Medium = 3
Intermediate = 2
Large = 1
Extra Large = 1
Giant = 1

About Kennel size (Guidance only):
Extra Small = for kennel size of 19 x 12 x 11 inches and 23 x 14 x 12 inches
Small / Medium = for kennel size of 21 x 17 x 18 inches and 27 x 20 x 19 inches
Intermediate = for kennel size of 32 x 22 x 23 inches
Large = for kennel size of 36 x 24 x 26 inches
Extra Large = for kennel size of 40 x 27 x 30 inches
Giant = for kennel size of 48 x 32 x 35 inches

Source: IPATA/UA

How To Measure Your Dog When Buying A New Kennel.

This is Guidance how to measure your dog when buying a new kennel for traveling. This measurements is minimum requirements. Taken from British Airways Guidance, but also a requirements from IATA.

Click the image below to enlarge.