The Energy Iron Calculator shows you exactly how much iron you get from a serving of food — and how iron-dense that food is for the calories it costs. Enter a food's iron and energy values (or pick a preset), set your serving size, and the tool returns iron per serving, energy per serving, iron per 100 kcal, and the percentage of your daily iron target that serving covers.
The "iron density" figure (mg of iron per 100 kcal) is especially useful if you're planning meals on a calorie budget, following a vegetarian or vegan diet, or trying to fix low energy levels on a restricted calorie intake. Because iron needs vary — 8 mg/day for most adult men, 18 mg/day for most women of reproductive age — the tool lets you choose the target that fits you.
Use a preset food from the list, enter custom values from a label, or do both: the maths updates instantly when you hit calculate.
🧮 Energy–Iron Calculator
Find the iron in your portion — and how much iron you get per calorie.
⚙️ Advanced: iron target & daily calorie budget
How to Use This Tool
Start by picking a food from the preset dropdown — the iron and energy fields fill in automatically with typical values from food-composition databases. If your food is not listed, choose "Custom values…" and enter the numbers from the nutrition label or a trusted database such as the USDA FoodData Central. Then set a serving size in grams, pick your energy unit (kcal or kJ), and press Calculate.
Inside the Advanced panel you can change the iron target used for the percentage figure — the default is 18 mg, the US Daily Value and the RDA for most women of reproductive age. If you also enter a daily calorie budget, the tool will estimate how many grams of that food you would need to hit your iron target within that budget.
Formula Explained
All three headline numbers come from simple proportions based on the food's values per 100 g:
- Iron per serving (mg): iron per 100 g × serving size (g) ÷ 100
- Energy per serving (kcal): energy per 100 g × serving size (g) ÷ 100
- Iron density (mg per 100 kcal): iron per serving ÷ calories per serving × 100
- Target coverage (%): iron per serving ÷ daily iron target × 100
When you enter energy in kilojoules, the calculator converts to kilocalories first using 1 kcal = 4.184 kJ, so the iron-per-100-kcal figure stays comparable across units.
Reference Table: Iron Density of Common Foods
Values are approximate and based on generic cooked or prepared foods from the USDA FoodData Central (per 100 g edible portion). Always prefer the label or the database for the exact product you are using.
| Food | Iron (mg / 100 g) | Energy (kcal / 100 g) | Iron (mg / 100 kcal) |
|---|---|---|---|
| Beef liver, cooked | 6.5 | 175 | 3.7 |
| Oysters, cooked | 6.8 | 163 | 4.2 |
| Fortified breakfast cereal | 14.0 | 380 | 3.7 |
| Dark chocolate (70–85%) | 11.9 | 598 | 2.0 |
| Pumpkin seeds | 8.8 | 559 | 1.6 |
| Spinach, cooked | 3.6 | 23 | 15.7 |
| White beans, cooked | 3.7 | 139 | 2.7 |
| Lentils, cooked | 3.3 | 116 | 2.8 |
| Chickpeas, cooked | 2.9 | 164 | 1.8 |
| Beef steak, lean | 2.6 | 217 | 1.2 |
| Tofu, firm | 2.2 | 144 | 1.5 |
| Quinoa, cooked | 1.5 | 120 | 1.3 |
Leafy greens and liver top the iron-per-calorie list, while low-iron staples such as quinoa still contribute useful amounts because people eat them in large portions.
Tips for Better Iron Absorption
- Pair plant iron with vitamin C: adding vitamin C-rich foods (citrus, peppers, broccoli, tomatoes) can increase non-heme iron absorption several-fold.
- Be careful with tea and coffee: polyphenols in tea, coffee, and red wine inhibit iron absorption when consumed with a meal; a 1-hour gap is an easy compromise.
- Heme vs non-heme: iron from meat, fish, and poultry is absorbed more efficiently, but it also helps your gut absorb iron from plant foods eaten in the same meal.
- Calcium timing: large doses of calcium can interfere with iron absorption, so consider taking calcium supplements at a different time of day.
- Cook with cast iron: acidic foods like tomato sauce cooked in a cast-iron pan pick up measurable amounts of iron.
Frequently Asked Questions
What is the difference between the 18 mg default and an RDA? The 18 mg figure is the Daily Value used on US nutrition labels (based on an adult reference diet) and the RDA for most adult women aged 19–50. Men need about 8 mg/day, pregnant women about 27 mg/day, and postmenopausal women about 8 mg/day. The Advanced panel lets you set any target.
Is a high iron-per-100-kcal figure always better? Not necessarily. The number describes iron density, not overall diet quality. A food with 15 mg per 100 kcal can still contribute little iron in a realistic portion, and very dense sources like liver should be eaten in moderation because of their high vitamin A content.
Can you get too much iron? Yes. The tolerable upper level for adults is about 45 mg/day from food, and people with hereditary hemochromatosis (a common inherited condition) absorb iron too eagerly. If you regularly take iron supplements, discuss it with a doctor first.
Which sources should I check for better numbers? For packaged foods, read the nutrition label. For whole foods, the USDA FoodData Central is the most reliable free database, while the Australian Nutrient Reference Values and EFSA opinions are helpful for targets outside the US. For single foods, try our tilapia iron calculator or cappuccino iron calculator to see serving-based iron results for those specific items.