The size determines the number of joints you can roll. A regular joint contains roughly 0.5g on average. Weed ounces weigh about 28 grams, so you can roll about 56 joints.
Rolling smaller ones will likely result in more, while rolling bigger ones will result in fewer. How much weed you use per joint can affect the total count. Remember that individual rolling styles and habits also matter. As a result, you could have anywhere from 40 to 60 joints.