Just do the math. The answer is hidden.
A pothead can get high for about 4-5 days with a quarter bag, 28 grams. A quarter bag will roll about 12-18 joints. And they are not big joints.
Or you can say, a pothead typically smokes half a joint to get high. A high lasts 1 1/2 to 2 hours.
Your math is a bit off. Your estimate is at least twice too high.