In an adult man, there is about how much grams of hemoglobin in the circulating blood?
About 900g of hemoglobin is present in the circulating blood of an adult man.
Also know:

The erythrocytes carry hemoglobin in the circulation. They are biconcave disks because of the protein called as spectrin.
In humans, the RBCs survive in the circulation for an average of 120 days.
The average normal red blood cell count is 5.4 million/ L in men and 4.8 million/ L in women.
1g of hemoglobin yields 35mg of bilirubin.
350
500
900
1000