# How can I calculate osmolarity of dextrose?

$P = c R T$
Rearranging this expression allows you to calculate the concentration from a measured osmotic pressure (differential pressure across a semi-permeable membrane). You can then convert c to molarity (divide by ${10}^{6} \frac{L}{m} ^ 3$). The result will be very close to the molality if the solvent is water and the solution is dilute, because because 1 L of water has a mass very close to 1 kg.