Unit of measurement for determining the amount of ointment, measured from the fingertip to the distal interdigital fold - this makes about 0.5 g of ointment for a diameter of the ointment strand of 5 mm. For cream (instead of ointment) minimally higher amount required. see illustration from Infectopharm Patient Guide.
1 FTU is sufficient for about 200-300 cm2 of skin surface. This surface area corresponds approximately to the size of one to two palms. According to the rule of nine from burn medicine, 1 palm covers about 1% of the body surface.
As a rule of thumb or "rule-of-hand", an area of 2 hands (approx. 2% of the body surface) should be treated with 1 FTU (approx. 0.5 g). This means that between 40-50 FTUs are necessary for a whole body therapy.
Body regimens have been developed that suggest the respective number of FTU per limb, etc. For children, other FTU dosages per limb etc. apply.
Gelmetti C et al. (2014) Atopic dermatitis - all you can do from the outside. Br J Dermatol. Jul 170 Suppl 1:19-24.
Long CC et al (1998) A practical guide to topical therapy in children. Br J Dermatol. 138: 293-296