This osmolarity is evenly distributed in the body, and is used to estimate the new volumes of ICF and ECF, respectively:formula_4where:*VICF a = Intracellular fluid volume after fluid loss*nICF a = Amount of substance in ICF after fluid loss*Osma = Body osmolarity after loss*VICF b = Intracellular fluid volume before fluid loss (approximately 40% of body weight, or subtracting ECF from TBW)*Osmb = Body osmolarity before loss (almost equal to plasma osmolality of 275-299 milli-osmoles per kilogram)*nlost K+ = Amount of substance of lost potassiumIn homologous manner:formula_5where:*VECF a = Extracellular fluid volume after fluid loss*nECF a = Amount of substance in ECF after fluid loss*VECF b = Extracellular fluid volume before fluid loss (approximately 20% of body weight, or by using inulin)*Osmb = Body osmolarity before loss (almost equal to plasma osmolality of 275-299 milli-osmoles per kilogram)*nlost K+ = Amount of substance of lost potassium5.