How much tissue is actually removed in an endometrial biopsy?

Not much but enough. Very little tissue is removed during an endometrial biopsy but multiple studies show that the amount is adequate to make an accurate diagnosis. The main purpose is to rule out cancer or premalignant lesions called endometrial hyperplasia.
Endometrial biopsy. Very little. A strip of tissue that is the thickness of a normal pencil lead and about 1 inch long.