18 milligrams 
Iron Requirements. Adult women between the ages of 19 and 50 need 18 mg of iron each day, and men the same age require 8 mg, according to the recommendations of the Institute of Medicine's Food and Nutrition Board. The recommendation for both men and women 51 or older is only 8 mg. Iron is measured in milligrams. The amount you need depends on your age, gender, body size, and lifestyle. In general, though, you can use these guidelines to determine how much iron you need. 1  Girls age 9-13: 8 mg/day. 2  Girls age 14-18: 15 mg/day. A 1-cup serving of green vegetables provides 1-3 milligrams of iron, depending on which vegetable you choose. A 1/2-cup serving of beans provides 2-3 milligrams. A bowl of a typical iron-fortified cereal has 18 milligrams. How much iron do you need? The recommended dietary allowance for adult males and for women over 50 is 8 milligrams per day. For women aged 19-50, the RDA is 18 milligrams per day (it’s higher to compensate for menstrual losses). In addition to supplements, you need to eat iron-rich foods every day. If you are taking calcium supplements as well as iron, talk with your pharmacist or dietitian about the best time of day to take them. Calcium may decrease the amount of iron that is absorbed by your body from a supplement. The iron in plants is called nonheme iron. Its absorption depends on how much iron is in your body already. That is, if you are low in iron, your body absorbs more of it from the foods you eat. If you already have plenty of iron in your body, nonheme iron is less absorbable. That’s good. It means you’ll get the iron you need without overdoing it. Males of average height have about 4 grams of iron in their body, females about 3.5 grams; children will usually have 3 grams or less. These 3-4 grams are distributed throughout the body in hemoglobin, tissues, muscles, bone marrow, blood proteins, enzymes, ferritin, hemosiderin, and transport in plasma.
http://www.livestrong.com/article/228006-how-much-iron-supplement-should-i-take-every-day/ http://youngwomenshealth.org/2013/12/06/iron/ http://www.vegetariantimes.com/article/ask-the-doc-iron-how-much-is-enough/ http://www.healthlinkbc.ca/healthfiles/hfile68c.stm http://www.vegetariantimes.com/article/ask-the-doc-iron-how-much-is-enough/ http://www.irondisorders.org/how-much-iron-is-in-the-body/
how much iron you need a day