From Their Web Site:
What are the restrictions and requirements for carry–on baggage?
Carry-on bags must comply with the following baggage regulations:
Each e-ticketed passenger is allowed to carry on the aircraft one bag
plus one personal item.
The exterior dimensions for a carry-on bag must not exceed 9" H x 14" W x 22" D. This measurement includes wheels, pockets, handles and decorations.
The bag must be able to fit under your seat or in the overhead compartment.
Examples of personal items include:
Male or female purse
Briefcase
Laptop computer
Camera case
Diaper bag
Portable electronic devices of similar or smaller size to items listed above
The exterior dimensions for a personal item must not exceed 9" H X 16" W X 19" D (this measurement includes wheels, pockets, handles and decorations)
The personal item must be placed under the seat in front of you
Examples of additional items that are allowed on the aircraft, in addition to the free baggage allowance, include:
Food items for immediate consumption
Mobility aids or assistive devices, such as wheelchairs, walkers, canes, crutches, strollers, etc.
One box or bag of duty free merchandise
A coat or jacket
An umbrella
One item of reading material
What are the restrictions and requirements for checked baggage?
Passengers wishing to check luggage will be charged a per person, per bag, per segment Baggage Fee. All Baggage Fees are non-refundable. Applicable fees will be applied for those bags exceeding the 50 lbs. weight limit and eighty inches size limit. The total number of bags allowed may not exceed 5 per passenger. No baggage more than 100 lbs. will be accepted.
Review Allegiant's Luggage Limitations of Liability