gas tank size for 97 GT??

I know the Fox tanks are 15.4 gallons. not sure if they made them bigger in the SN95's.

The way i calculate my MPG is to fill my tank completely and push the trip reset button. Then i drive around and go fill my tank again. I look on the pump to see the gallons i used and then use the milage on my trip reset to see how far i went.