Iron is an essential mineral that supports oxygen transport, energy metabolism, and immune function. While red meat is often highlighted as a top source, many vegetables — especially leafy greens, legumes, and certain roots — provide significant amounts of non-heme iron. However, the iron content varies widely by vegetable type, serving size, and preparation method.
This Vegetable Iron Calculator helps you quickly estimate the iron content of common vegetables based on your chosen portion. Whether you're planning a plant-based diet, tracking micronutrients, or simply curious about your daily intake, this tool gives you a reliable estimate in milligrams. Use it to compare spinach vs. kale, or to see how much iron a cup of cooked lentils provides. No more guesswork — just clear, actionable nutrition data.
🥦 Vegetable Iron Calculator
How to Use This Tool
Select a vegetable from the dropdown menu, then enter your serving size in grams, ounces, or cups. Click "Calculate Iron" to see the total iron content in milligrams. Use the quick-fill buttons for common portion sizes like 30 g (1 oz), 85 g (3 oz), or 1 cup. The breakdown shows the iron density per 100 g and the step-by-step calculation. You can compare different vegetables by changing the selection and recalculating — for example, see how much more iron cooked spinach provides compared to raw kale for the same serving size.
Iron Content Reference Table
| Vegetable | Iron (mg / 100 g) | Notes |
|---|---|---|
| Spinach (raw) | 2.71 | High in oxalates, which reduce absorption |
| Spinach (cooked) | 3.57 | More concentrated due to water loss |
| Kale (raw) | 1.47 | Good source with moderate oxalates |
| Swiss Chard | 1.80 | Also rich in magnesium and vitamin K |
| Lentils (cooked) | 3.33 | Excellent plant source, also high in protein |
| Chickpeas (cooked) | 2.89 | Versatile legume, good for salads and stews |
| Seaweed (dried) | 28.66 | Very high, use sparingly due to iodine content |
| Broccoli | 0.73 | Moderate source, also high in vitamin C |
| Green Peas | 1.47 | Good source, also provides fiber |
| Potato (with skin) | 0.81 | Skin contains most of the iron |
How It Works
The calculator uses USDA food composition data for iron content per 100 grams of each vegetable. When you enter a serving size, it converts to grams (if needed) and applies the formula: Iron (mg) = (Iron per 100 g / 100) × Serving (g). For cup measurements, we use standard density conversions (grams per cup) specific to each vegetable — for example, 1 cup of raw spinach weighs about 30 g, while 1 cup of cooked spinach weighs about 180 g due to water loss during cooking. The iron density values are sourced from the USDA FoodData Central database, which provides reliable nutrient profiles for thousands of foods.
Worked Examples
Example 1: 1 cup of cooked spinach (180 g). Iron per 100 g = 3.57 mg. Iron = (3.57 / 100) × 180 = 6.43 mg. That's about 36% of the daily value for adult women (18 mg) and 80% for adult men (8 mg).
Example 2: 85 g (3 oz) of raw kale. Iron per 100 g = 1.47 mg. Iron = (1.47 / 100) × 85 = 1.25 mg. That's about 7% of the daily value for women and 16% for men.
Example 3: 200 g (7 oz) of cooked lentils. Iron per 100 g = 3.33 mg. Iron = (3.33 / 100) × 200 = 6.66 mg. This single serving provides 37% of the daily value for women and 83% for men, making lentils one of the most iron-dense plant foods.
Tips for Maximizing Iron Absorption
Non-heme iron from plants is less absorbable than heme iron from meat. To boost absorption: pair iron-rich vegetables with vitamin C (e.g., squeeze lemon on spinach salad, add bell peppers to lentil soup, or eat broccoli with tomatoes). Avoid drinking tea or coffee with meals, as tannins inhibit absorption — wait at least one hour after eating. Cooking in a cast-iron skillet can add 1-2 mg of iron per serving, especially with acidic foods like tomatoes. Soaking and sprouting legumes reduces phytates that block iron uptake. Also, cooking vegetables like spinach and kale reduces oxalate content, which can improve iron absorption by up to 20%.
Frequently Asked Questions
Q: Can I get enough iron from vegetables alone? Yes, with careful planning. The recommended daily intake is 8 mg for men and 18 mg for women (premenopausal). A well-planned plant-based diet with lentils, spinach, chickpeas, and fortified foods can meet these targets. For example, a day's menu might include 1 cup cooked lentils (6.66 mg), 1 cup cooked spinach (6.43 mg), and 1 cup chickpeas (4.74 mg) — totaling over 17 mg, which meets the needs for most people.
Q: Why does cooked spinach have more iron per 100 g than raw spinach? Cooking removes water, concentrating the nutrients. Raw spinach is about 91% water, while cooked spinach is about 83% water. So the iron content per 100 g increases from 2.71 mg to 3.57 mg, even though the absolute amount of iron in the original raw leaves hasn't changed.
Q: Is seaweed a good source of iron? Dried seaweed is extremely high in iron (28.66 mg per 100 g), but it's typically eaten in small amounts (5-10 g per serving). A 10 g serving provides about 2.87 mg of iron. However, seaweed also contains high levels of iodine, so it should be consumed in moderation, especially for people with thyroid conditions.
Q: How accurate are these values? The iron content of vegetables can vary based on soil quality, growing conditions, variety, and cooking method. The values in this calculator are averages from the USDA FoodData Central database and are intended for general dietary planning. For precise medical or clinical purposes, consult a registered dietitian or use laboratory analysis.