Osmolality, Serum Unit Converter

Serum osmolality measures the concentration of dissolved particles in the liquid portion of your blood. These particles include electrolytes like sodium and chloride, as well as glucose and urea.

It reflects the balance between water and solutes in your body. Sodium is the single largest contributor to serum osmolality, so changes in sodium levels are the most common reason osmolality shifts.

The normal range is 275–295 mOsm/kg. Your body works to keep osmolality within this narrow window through hormones like antidiuretic hormone (ADH) and the thirst mechanism.

Serum osmolality is not produced by a single organ. It is determined by the total concentration of dissolved solutes in the blood, primarily sodium (and its accompanying anions), along with glucose and urea. The kidneys, guided by ADH from the pituitary gland, are the main regulators of osmolality by adjusting water reabsorption.