A platelet count is a lab test to measure how many platelets you have in your blood. Platelets are parts of the blood that helps the blood clot. They are smaller than red or white blood cells. A normal platelet count ranges from 150,000 to 450,000 platelets per microliter of blood. Having more than 450,000 platelets is a condition called thrombocytosis; having less than 150,000 is known as thrombocytopenia. You get your platelet number from a routine blood test called a complete blood count (CBC).