me assume yu meen a cylinder with diameter=7 ft & leng=7 ft+4 inch... volume=leng* base area... area=pi*rad*rad=3.141592654*3.5*3.5... area=12.25*3.14159265=38.48450996... leng=7ft+3inch=7.25 ft... volume=7.25*38.48450996=279.0126972 kubik ft 1 kube ft=7.480681 gallon... 279.0126972*7.480681=2087.204983 gallon... or bout 2087 gallon