The coin book says a silver dollar was minted at 0.77344 troy ounce, the half dollar at 0.36169 troy ounce, so a silver dollar has as much silver as 2.1384 silver halves. Be sure to know this in SHTF conditions, as you can sell the tenderer of a silver dollar 15 ears of corn while the tenderer of 2 silver halves only gets 14. Remember, though, that while the mint spec for 2 silver halves is 0.72338 troy ounce of Ag it will be less, due to abrasion. Four average circulated silver quarters weigh in at 0.715 troy ounce of Ag and halves do a little better.