Iron from plants behaves differently than iron from meat, and leafy greens need a little extra attention. This Green Iron Calculator helps you quickly estimate the iron in spinach, kale, Swiss chard, bok choy, broccoli and other common greens based on the portion you actually eat. It is built for vegetarians, vegans, athletes and anyone curious about their micronutrient intake.
Enter your portion in grams, adjust the number of servings, pick a vegetable, and choose your meal context. The calculator returns total iron, its percentage of the daily value (18 mg for adults), and an approximate absorbed-iron estimate using typical non-heme absorption rates. That makes it easy to compare a raw salad with a cooked side dish, or to see how vitamin C changes the picture.
With quick presets and a copyable result, this tool takes the guesswork out of hitting your iron goals from vegetables.
Green Iron Calculator
Estimate iron from leafy greens and your daily value.
📊 Results
How to Use This Tool
Select the leafy green that matches your meal from the dropdown. Enter the portion in grams (100 g is about one large handful of raw spinach or half a cup of cooked greens), set the number of servings, and choose the meal context that best describes what else you ate. Click Calculate to see total iron, the share of the 18 mg daily value, and an absorbed estimate. Use the preset buttons to jump to common serving sizes.
How the Absorption Estimate Works
Iron in plants is non-heme iron, and the body absorbs only a fraction of it. The calculator applies a typical baseline absorption of 2% when no enhancers or inhibitors are present. Vitamin C can roughly double absorption, so the tool uses 3.5% when a vitamin C source is part of the meal. Tea and coffee contain tannins that reduce absorption, so the rate drops to 1.4%. When vitamin C is combined with tea or coffee, the tool uses 2.5% as a middle-ground estimate.
The absorbed estimate is calculated as: total iron (mg) × absorption rate ÷ 100. These rates are population averages, not precise predictions for a specific person.
Worked Examples
Example 1: 150 g of cooked spinach (3.57 mg iron per 100 g) eaten with lemon juice. Total iron = 3.57 × 150 ÷ 100 = 5.36 mg. With a 3.5% absorption rate, absorbed iron ≈ 0.19 mg.
Example 2: 85 g of raw kale (1.60 mg per 100 g) with coffee after the meal. Total iron = 1.60 × 85 ÷ 100 = 1.36 mg. At 1.4% absorption, absorbed iron ≈ 0.02 mg.
Iron Reference Values for Leafy Greens
| Vegetable | Iron (mg per 100 g) |
|---|---|
| Spinach, cooked | 3.57 |
| Spinach, raw | 2.71 |
| Swiss chard, cooked | 1.90 |
| Kale, raw | 1.60 |
| Green peas, cooked | 1.29 |
Values reflect standard USDA reference data. Actual iron content varies with soil, variety, and cooking method.
Common Mistakes to Avoid
- Entering ounces instead of grams — use a kitchen scale or the preset buttons.
- Forgetting to adjust servings when eating a double portion.
- Assuming all vitamin C sources have equal effects; the absorption rates are averages, not exact values.
- Confusing total iron with absorbed iron. The daily value is based on total iron, but your body will absorb much less from plants.
Frequently Asked Questions
Why is the absorbed iron estimate so low?
Non-heme iron from plants is absorbed less efficiently than heme iron from meat. Absorption rates of 1–4% are typical, which is why pairing greens with vitamin C and avoiding tea or coffee with the meal can help.
Should I worry about too much iron from vegetables?
Food sources of non-heme iron rarely cause iron overload in healthy people because absorption is tightly regulated. The main concern is low iron status, especially for menstruating women and people on plant-based diets.
Are cooked greens better than raw?
Cooking can increase iron concentration per gram because water is lost, but it can also leach some iron into cooking water. Both forms count toward your intake; choose what you enjoy.
For more detailed nutrient data, see the USDA FoodData Central database.