How Much Iron Does Spinach Contain and What Factors Affect or Increase Iron Absorption In the Body? July 11, 2014 by Karen Hill | Filed Under: Science The United States Department of Agriculture states that a 180 g serving of boiled spinach contains 6.43 mg of iron. The reason you should you always use a stainless steel knife to cut your spinach is intriguing and is a major stumbling block to the fortification of food with iron. Remember that a lack of iron is the world’s most prevalent nutritional deficiency.