How BIG is a stock fuel tank on a 96 s-10?

When i feel up my tank when it says empty, it only holds 10 gal. at the most, and i get about 240 miles from F to E. I know that is not right for 1 it looks way bigger than my 10 gal. fish tank and before i put a new fuel pump and sen. unit in i would go alot longer on a tank of gas but it also maybe cuase gas prises have gone up. So just please let me in on how many gallons a stock fuel tank will hold. thanks