Iron Dosage Calculator
Calculate safe iron supplement dosages based on weight and age. Convert between different iron salt forms, determine elemental iron content, and compare to Recommended Dietary Allowances (RDA).
Quick Facts About Iron Supplements
- • Elemental iron content varies by iron salt form (20-33% of total weight)
- • Adult females need 18mg/day RDA, males need 8mg/day
- • Take iron with vitamin C to enhance absorption, avoid with calcium or tea
- • Common side effects include constipation and stomach upset
Enter Information
Common: Ferrous Sulfate 325mg tablet
Dosage Results
Elemental iron above 45mg may cause GI side effects. Take with food and consider dividing into multiple doses. Consult healthcare provider.
Iron Absorption Tips
- • Take with vitamin C to enhance absorption
- • Avoid taking with calcium or tea (reduces absorption)
- • Take on empty stomach if tolerated, or with food if needed
- • Space out from other medications by 2 hours
Common Iron Supplements
- • Ferrous Sulfate 325mg = 65mg elemental iron
- • Ferrous Gluconate 325mg = 39mg elemental iron
- • Ferrous Fumarate 325mg = 107mg elemental iron
What Is Elemental Iron?
Elemental iron refers to the actual amount of pure iron contained in an iron supplement, as opposed to the total weight of the iron compound or salt. Iron supplements are sold as iron salts - chemical compounds combining iron with other substances like sulfate, gluconate, or fumarate. For example, a common 325mg ferrous sulfate tablet contains only 65mg of elemental iron (20%), with the remaining 260mg being sulfate. This distinction is critical because therapeutic recommendations and Recommended Dietary Allowances (RDA) are based on elemental iron, not total tablet weight.
Different iron salts contain different percentages of elemental iron: ferrous sulfate provides 20%, ferrous gluconate provides 12%, and ferrous fumarate provides 33%. When your doctor prescribes "60mg of iron daily," they mean 60mg of elemental iron. To get this amount from ferrous sulfate, you'd need 300mg total compound. From ferrous gluconate, you'd need 500mg total compound. Understanding this conversion is essential for taking the correct dose and comparing different iron supplement products.
Frequently Asked Questions
What is the difference between elemental iron and iron salt?
Iron supplements contain iron salts (ferrous sulfate, ferrous gluconate, ferrous fumarate) which are compounds of iron combined with other substances. Elemental iron refers to the actual amount of pure iron in the supplement. For example, a 325mg ferrous sulfate tablet contains only 65mg of elemental iron (20%), with the remaining 260mg being sulfate. When determining dosage, always calculate based on elemental iron content, not total tablet weight. Different iron salts have different percentages of elemental iron: ferrous sulfate 20%, ferrous gluconate 12%, and ferrous fumarate 33%.
How much iron do I need daily?
Daily iron needs vary by age, gender, and life stage. Adult men and postmenopausal women need 8mg daily. Menstruating women need 18mg daily due to blood loss. Pregnant women require 27mg daily to support increased blood volume and fetal development. Teens need 11-15mg depending on gender. Infants 7-12 months need 11mg. These are Recommended Dietary Allowances (RDA) for total iron from food and supplements combined. People with iron deficiency anemia may need therapeutic doses of 100-200mg elemental iron daily under medical supervision, far exceeding RDA levels.
What are common side effects of iron supplements?
Iron supplements frequently cause gastrointestinal side effects including constipation (most common), nausea, stomach upset, dark or black stools (harmless but expected), diarrhea, and metallic taste. Higher doses cause more side effects. To minimize discomfort: start with low doses and gradually increase, take with food (though this reduces absorption), choose slow-release formulations, drink plenty of water, increase dietary fiber for constipation, or try different iron salt forms (some people tolerate ferrous gluconate better than sulfate). If side effects are severe, consult your doctor about dose adjustments or alternative treatments.
When is the best time to take iron supplements?
For optimal absorption, take iron supplements on an empty stomach 1 hour before or 2 hours after meals, preferably in the morning. However, if you experience stomach upset, take with food - slightly reduced absorption is better than not taking it at all. Pair iron with vitamin C (orange juice, citrus fruit) to enhance absorption. Avoid taking iron with calcium supplements, dairy products, coffee, tea, or antacids within 2 hours, as these significantly reduce absorption. For high doses (over 45mg elemental iron), split into 2-3 smaller doses throughout the day to improve tolerance and absorption.
How long does it take for iron supplements to work?
Timeline for iron supplement effects varies by severity of deficiency and dosage. Some people feel increased energy within 1-2 weeks as hemoglobin begins rising. However, full restoration of iron stores takes 3-6 months of consistent supplementation. Blood tests typically show improvement in hemoglobin within 4 weeks, but ferritin (iron stores) takes longer to normalize. Continue taking iron supplements for the full duration prescribed by your doctor, even after feeling better - stopping too soon can allow deficiency to return. Follow-up blood work confirms when iron levels are adequately replenished and supplementation can be adjusted or stopped.
Can I take too much iron? What is the upper limit?
Yes, excessive iron intake can be harmful. The Upper Tolerable Limit (UL) for adults is 45mg elemental iron daily from supplements. Higher therapeutic doses are safe under medical supervision. Acute iron poisoning from massive overdose (like a child swallowing many adult iron pills) is a medical emergency requiring immediate treatment. Chronic iron overload from long-term excessive supplementation can damage the liver, heart, and pancreas. Never exceed recommended doses without medical guidance. Iron toxicity is especially dangerous for children - always keep iron supplements out of reach and use child-resistant bottles. If overdose occurs, call poison control immediately.
Does iron interact with medications?
Iron interacts with numerous medications, reducing effectiveness of both the iron and the medication. Major interactions include: antibiotics (tetracyclines, quinolones - separate by 2 hours), levothyroxine thyroid medication (separate by 4 hours), levodopa for Parkinson's (separate by 2 hours), bisphosphonates for osteoporosis (separate by 2 hours), proton pump inhibitors and antacids (reduce iron absorption), and calcium supplements (compete for absorption). Always inform healthcare providers about iron supplementation when prescribed new medications. Read medication labels for iron interaction warnings. Maintain 2-4 hour spacing between iron and other medications unless specifically instructed otherwise.
Should I take iron if I eat a lot of iron-rich foods?
Dietary iron from food is generally safer than supplemental iron because the body naturally regulates absorption based on needs. Even eating iron-rich foods (red meat, spinach, legumes, fortified cereals) daily rarely causes toxicity. However, supplements bypass some regulatory mechanisms. If you eat abundant iron-rich foods and have normal iron levels on blood tests, you likely don't need supplements. Supplementation is warranted for diagnosed iron deficiency anemia, documented low iron levels, increased needs (pregnancy, heavy menstrual bleeding), or absorption problems. Never self-prescribe iron supplements - get blood work to confirm deficiency before starting supplementation.
Why does iron cause constipation and what can I do about it?
Iron supplements cause constipation because iron irritates the intestinal lining, slowing gut motility and hardening stool. To combat iron-induced constipation: increase water intake (8-10 glasses daily), boost dietary fiber from fruits, vegetables, and whole grains, exercise regularly to stimulate bowel movements, consider stool softeners (not laxatives) if needed, try slow-release or enteric-coated iron formulations, switch to ferrous gluconate which may be gentler, or split high doses into smaller amounts throughout the day. If constipation becomes severe or painful, consult your doctor about dose adjustment or alternative iron formulations like iron polysaccharide complex.
Are there different types of iron supplements and which is best?
Common iron supplement types include ferrous sulfate (most common, 20% elemental iron, often causes GI upset), ferrous gluconate (12% elemental iron, better tolerated, requires higher doses), ferrous fumarate (33% elemental iron, highest concentration), iron polysaccharide complex (better tolerated, less constipation, more expensive), heme iron polypeptide (derived from animal sources, better absorbed), and carbonyl iron (pure elemental iron, safer in overdose). "Best" depends on individual tolerance, absorption, cost, and medical needs. Most doctors start with ferrous sulfate due to effectiveness and low cost, switching to alternatives if side effects are problematic. Discuss options with your healthcare provider.