A 325-mg tablet of ferrous sulfate heptahydrate has 65 mg (20%) of elemental iron A 325-mg tablet of ferrous gluconate has 39 mg (12%) of elemental iron A 325-mg tablet of ferrous fumarate has 107.25 mg (33%) of elemental iron 200 mg ferrous sulfate, dried, has 65 mg (33%) of elemental iron