If you are talking about fluid capacity for filter and fluid change:
19 quarts. Cheapest is to buy the 5 gallon pail which leaves you one quart left over. This assumes you have the shallow sump. The Allison dealer can tell you from the serial number on the driver's side of the transmission.
The Allison filter kit comes with instructions and gaskets you will need.
Ex: 2003 Alpine 38FDDS. Ex: 1997 Safari Sahara. Ex: 1993 Foretravel U240