==== What size under-seat bag, by airline ====
^Airline^  Dimensions in inches  ^  Capacity in Liters  ^
|Alaska Airlines|  14 x 12 x 9  |24.7L|
|Allegiant Air|  16 x 15 x 7  |27.5L|
|American Airlines|  18 x 14 x 8  |33.0L|
|Delta Airlines|  17 x 16 x 7.5  |33.4L|
|Frontier Airlines|  18 x 14 x 8  |33.0L|
|JetBlue Airlines|  17 x 13 x 8  |28.9L|
|Southwest Airlines|  18.5 x 13.5 x 8.5  |34.7L|
|Spirit Airlines|  18 x 14 x 8  |33.0L|
|United Airlines|  17 x 10 x 9  |25.0L|