Van Persie has scored 10 goals for United since his summer move from Arsenal - helped significant by his forming an immediate understanding with Rooney.
Van Persie told the club's official website: "I call it a nine and a half because you have two positions, the nine and the 10, and we are both nine and a half.
"We are just helping each other out. We both play behind and a bit higher up. It seems to be working well and I am very happy with Wayne - hopefully we can keep it going."