MOST IMPORTANT FORMULA USE IN POSOLOGY CALCULATION 

1. Young’s Rule: Child dose = [Age X Adult dose] / (Age + 12) 

2. Couling’s Rule: Infant dose = [Age (at next birthday) X Adult dose] / 24

3. Fried’s Rule: Infant dose = [Age (in months) X Adult dose] / 150 

4. Clark’s Rule: Child dose = [Weight (in lbs) X Adult dose] / 150 

DENSITY = MASS / VOLUME 

SPECIFIC GRAVITY (Sp. gr.) 

Sp. gr. = Wt / V 

Sp. vol = V / Wt thus sp. volume = 1 / sp. gr 

Wt. of the liquid = sp. gr. of liquid X volume of the liquid 

Volume of a liquid = Wt of liquid / sp. gr. 

Strength X Volume = Strength X Volume 

CALCULATION OF TEMPERATURE 

9 X oC = 5 X oF -160 

Proof Gallon = Wine gallon X Proof strength / 50% 

ISOTONICITY 

Ø Sodium chloride 0.90% 

Ø Dextrose 5.00% 

Ø Boric acid 1.73% 

FREEZING POINT DEPRESSION OF NORMAL SALINE IS 0.52 

The equivalent weight = Molecular weight / valency 

Mosmol = m moles X no of ions = (wt in mg / m wt) X no of ion