Collard greens are one of the most nutrient-dense leafy vegetables you can add to a plate — and their iron content is a big part of the appeal, especially for plant-based eaters, vegans, and anyone watching their daily micronutrient targets. The Collard Iron Calculator converts your serving size into milligrams of iron and shows how that fits into the recommended Daily Value of 18 mg for most adults.
Because iron in collards is non-heme iron from plants, the amount you absorb depends on how the greens are prepared and what you eat alongside them. This calculator lets you choose raw, boiled, frozen, or canned collards and works with gram, ounce, or cup measurements — so you can quickly check a recipe, a meal, or a whole week of greens.
Use the results to compare collards with other iron sources, plan higher-iron meals, and understand how much cooked greens you actually need to move the needle on your daily iron intake.
🥬 Enter your serving
📊 Iron results
Step-by-Step Guide
Using the Collard Iron Calculator takes only a few seconds. First choose how you are measuring your greens — grams, ounces, or cups. If you are logging from a recipe, grams are the most precise; if you are estimating what is on your plate, cooked cups are more practical. Next, select the preparation that matches your collards: raw, boiled, frozen-cooked, or canned. Enter the number of units and press Calculate iron.
- Type a serving size into the amount field (for example, 150).
- Pick the matching unit: grams, ounces, cups chopped raw, or cups cooked.
- Choose the preparation method from the dropdown menu.
- Press Calculate to see milligrams of iron, percent of Daily Value, and the serving needed to reach 100% DV.
- Use Reset to start over, or Copy result to save the numbers to your clipboard.
The preset buttons — 100 g raw, 1 cup raw, 1 cup cooked, and 3 oz cooked — give you quick starting points so you can compare common serving sizes without typing.
Reference Table: Iron in Collard Greens
Iron content changes with water loss during cooking and with processing, so the same volume of greens can deliver very different amounts. The table below shows the values used in this calculator, based on USDA FoodData Central entries.
| Collard form | Iron per 100 g | Approx. iron per 1 cup |
|---|---|---|
| Raw, chopped | 0.47 mg | 0.17 mg (1 cup ≈ 36 g) |
| Boiled, drained | 0.54 mg | 0.92 mg (1 cup ≈ 170 g) |
| Frozen, cooked | 0.98 mg | 1.67 mg (1 cup ≈ 170 g) |
| Canned, drained | 1.03 mg | 1.75 mg (1 cup ≈ 170 g) |
How the Calculation Works
The calculator starts by converting your serving into grams. It then multiplies by the milligrams of iron per 100 grams for the preparation you selected, using this formula:
Iron (mg) = serving weight (g) × iron per 100 g ÷ 100For example, a 170 g cup of boiled collards delivers roughly 170 × 0.54 ÷ 100 = 0.92 mg of iron. The percent Daily Value is calculated against the 18 mg reference used by the FDA for nutrition labeling. To find the serving that reaches 100% DV, the calculator divides 18 mg by the iron density of your chosen form — for boiled collards that is about 3.3 kg of cooked greens, which shows why variety matters when building an iron-rich diet.
Worked Examples
Example 1: 1 cup of boiled collards (170 g).
170 g × 0.54 mg/100 g ÷ 100 = 0.92 mg iron → about 5% of the 18 mg Daily Value.
Example 2: 100 g of frozen cooked collards.
100 g × 0.98 mg/100 g ÷ 100 = 0.98 mg iron → about 5.4% of Daily Value.
Example 3: 3 oz (85 g) of raw chopped collards.
85 g × 0.47 mg/100 g ÷ 100 = 0.40 mg iron → about 2.2% of Daily Value.
Tips for Getting More Iron from Collards
- Pair collard dishes with a source of vitamin C — lemon juice, tomatoes, or bell peppers — to improve absorption of non-heme iron.
- Cook collards in a cast-iron skillet or pot; a small amount of iron can transfer into the food during cooking.
- Avoid drinking coffee or tea within an hour of an iron-rich meal, since tannins can reduce absorption.
- Don't overlook canned or frozen collards in the off-season — they are convenient and often higher in iron per 100 g than raw leaves because of water loss.
Frequently Asked Questions
Are collard greens a good source of iron? Yes, especially relative to their calorie count. A cooked cup delivers about 0.9 mg, and because greens are easy to eat in large volume, they make a meaningful contribution to daily intake for plant-based eaters.
Why is cooked collard iron per cup higher than raw? Cooking removes water and shrinks the leaves, so a cup of cooked greens contains several times more plant material — and therefore more iron — than a cup of raw leaves.
Is collard iron the same as meat iron? No. Collards contain non-heme iron, which is absorbed less efficiently than the heme iron in meat, fish, and poultry. Combining greens with vitamin C and avoiding inhibitors like tea at the same meal improves absorption.
What is the Daily Value for iron? The FDA uses 18 mg per day for nutrition labels. Individual needs vary — pregnant women need more, and some people with hemochromatosis need less. Use the percent DV as a rough guide, not a medical prescription. See the NIH Office of Dietary Supplements iron fact sheet for detailed guidance.
Limitations & Accuracy Notes
Iron values in this calculator come from USDA FoodData Central averages and can vary with cultivar, growing conditions, cooking water, and how tightly leaves are packed. The cup conversions assume standard chopped and drained servings, so treat the result as a reasonable estimate for meal tracking and comparing foods — not a laboratory measurement.