I don't measure it this way. I usually see how much juice is covering the top of my hand when i spray. When i feel it's enough, i stop spraying.
Usually 2 sprays on the same spot will do. The same applies when testing on other parts of my body (chest, neck etc).
It also all depends on how strong the scent is. You'll figure it out and adjust on the go. I wouldn't put that much calculation into it.