Botox is generally calculated by a unit method because it’s a liquid. Thick gels, like a dermal filler, are calculated per syringe, but this is not to be confused with per unit calculation of Botox. Botox is a unit amount based on the liquid that is drawn. The amount of Botox needed is determined based on your age, gender, and sex. Men generally need more botox than other genders, while older people generally require more Botox as well.