Tank Size ?

[MadMan-JaMeS]

am i right in thinking my tank which is

18 inches Tall
12 inches Wide
36 inches long

has a capacity of 24 Gallons ?

i looked on the volume calculator but couldn't work it out for sure any help please ?

 

[lym]

28 Gallons according to this website: http/animal-world.com/encyclo/information/calculate.htm