Haemoglobin is a protein found in the red blood cells that is in charge of delivering oxygen to all body tissues. On the other hand haematocrit is defined as the fraction of the erythrocyte.
Why are you interested in knowing the HCT if you already know the Hb? They are comparable only if red cells contain normal amounts of Hb (mean cell hemoglobin) is normal.
"With modern lab equipment, the hematocrit is calculated by an automated analyzer and not directly measured. It is determined by multiplying the red cell count by the mean cell volume. The hematocrit is slightly more accurate as the PCV includes small amounts of blood plasma trapped between the red cells. An estimated hematocrit as a percentage may be derived by tripling the hemoglobin concentration in g/dL and dropping the units.[5]" - wikipedia , "hematocrit"