A. Platelets are the tiny blood cells that help stop bleeding by binding together to form a clump or plug at sites of injury inside blood vessels. A normal platelet count is between 150,000 and 450,000 platelets per microliter (one-millionth of a liter, abbreviated mcL).The average platelet count is 237,000 per mcL in men and 266,000 per mcL in women. platelet count below 150,000 per mcL is called thrombocytopenia, while a platelet count over 450,000 is called thrombocytosis. Platelets seem to have a large backup capacity: blood typically still clots normally as long as the platelet count is above 50,000 per mcL (assuming no other problems are present).