Actually, this question is about the following sentence, which I have seen (in various forms) in numerous papers (e.g. this one and this one):

The American Academy of Pediatrics advises that formulas for normal infants should have an osmolarity no greater than 400 mOsm/L (approximately 450 mOsm/kg).

I searched Google up and down but could not find the calculation or the conversion between osmolarity and osmolality of infant formulas. I might be missing something, but does anyone know or can find the relationship between those two values?


From Wikipedia:

Osmolarity = osmolality * (ρsol − ca)


  • ρsol is the density of the solution in g/ml, which is 1.025 g/ml for blood plasma.[5]
  • ca is the (anhydrous) solute concentration in g/ml – not to be confused with the density of dried plasma

p.s. I am surprised that the osmolarity and osmolality differ that much in numeric value. For other (non-medical) purposes I considered them almost interchangeable.


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