Fennel bulb brings a light anise flavor to salads, soups, and roasted dishes — and a small but useful amount of dietary iron. This fennel iron calculator estimates how much iron you get from a given portion of fennel, whether you measure it in grams, ounces, sliced cups, or whole medium bulbs.
Choose a preparation and the tool will use an appropriate iron density, then show milligrams and the percentage of an 18 mg Daily Value reference. You can also adjust the daily value to match your own nutrition target, and a step-by-step breakdown explains each part of the calculation.
Fennel is not a heavy-hitting iron source compared with red meat or lentils, but it contributes to total intake — especially in plant-based diets. This calculator is useful for anyone monitoring iron, planning weekday meals, or comparing fennel with other vegetables.
🥬 Fennel Iron Calculator
Estimate the iron in fresh or cooked fennel bulb from your portion and preparation.
1 · Portion size
2 · Iron density
3 · Daily iron target
How to Use This Tool
Pick the unit that matches how you measure fennel — grams, ounces, sliced cups, or whole medium bulbs — then enter the portion. The calculator converts your portion to grams, applies the iron density, and shows both milligrams of iron and the percentage of your daily target. The default density is 0.73 mg per 100 g of raw bulb, but the preset buttons let you switch to boiled fennel (0.66) or a higher estimate (0.80) in one click.
You can also adjust the daily iron target from the default 18 mg to any value that reflects your own nutrition plan. The step-by-step breakdown at the bottom of the results shows exactly how the portion was converted and multiplied, which makes it easy to verify the math or reuse the method in a food diary.
How the Iron Calculation Works
The tool uses a simple three-step method. First, it converts your portion to grams using standard kitchen equivalents: 1 sliced cup ≈ 87 g and 1 medium bulb ≈ 234 g (or multiply ounces by 28.35 to get grams). Second, it calculates iron content with this formula:
Iron (mg) = Portion weight (g) × Iron density (mg per 100 g) ÷ 100
Third, it converts that result into a percentage of your daily target with this formula:
Percent of daily value = Iron (mg) ÷ Daily target (mg) × 100
Because the density is expressed per 100 g, dividing by 100 after multiplication keeps the units consistent. This same calculation pattern applies to any food, so you can substitute values from other nutrient databases whenever you want a custom estimate.
Worked Examples
Example 1 — Whole bulb in grams: A 250 g fennel bulb at 0.73 mg/100 g provides 250 × 0.73 ÷ 100 = 1.83 mg iron, or 1.83 ÷ 18 × 100 ≈ 10.2% of an 18 mg daily target.
Example 2 — Sliced cup: One sliced cup (87 g) provides 87 × 0.73 ÷ 100 = 0.64 mg, about 3.5% of the same target.
Example 3 — Boiled portion: A 150 g portion of boiled fennel at 0.66 mg/100 g provides about 0.99 mg, roughly 5.5% of an 18 mg target.
These examples show how the same tool works across different units and densities. Notice that a fennel-heavy salad might reach 2–3 mg of iron when paired with other vegetables — a meaningful contribution, though still far from the 18 mg reference.
Standard Iron Values for Fennel
| Fennel form | Iron per 100 g |
|---|---|
| Raw fennel bulb | 0.73 mg |
| Boiled fennel bulb | 0.66 mg |
| Fennel seed (dried) | 18.5 mg |
These values are estimates from nutrient databases such as USDA FoodData Central. If fennel is boiled in a large amount of water and the water is discarded, some minerals can leach into the liquid, which is why boiled values are often slightly lower than raw ones. Fennel seeds are much more iron-dense because drying removes water and concentrates nutrients, but they are usually used in small teaspoon amounts.
Tips for Tracking Iron
- Pair fennel with vitamin C-rich foods such as citrus, tomatoes, or bell peppers. Vitamin C helps your body absorb non-heme iron from plant sources.
- Track iron from all sources — legumes, fortified grains, greens, seeds, and nuts — because vegetables like fennel contribute modest amounts on their own.
- Watch for cooking habits that reduce iron content. Boiling in large amounts of water can lower mineral levels, while steaming and roasting tend to preserve more.
- Remember that the 18 mg Daily Value is a label reference for planning, not a one-size-fits-all target. Individual needs depend on age, sex, and health conditions, and clinical guidelines may differ.
Frequently Asked Questions
Is fennel a good source of iron?
Fennel bulb is a modest source of iron rather than a major one. A typical 100 g portion supplies under 1 mg, which is helpful for plant-based eaters who combine many small contributors, but a single serving alone won't meet a day's needs. Fennel does add flavor and fiber, so it earns a place in an iron-conscious diet even if it isn't the star of the meal.
Why is the default daily value 18 mg?
The U.S. Food and Drug Administration sets the Daily Value for iron at 18 mg for adults and children aged 4 and older on Nutrition Facts labels, based on reference values summarized in the NIH Iron Fact Sheet for Health Professionals. You can adjust the target in the calculator to match a personal plan, a pregnancy target, or a clinical recommendation.
Does cooking fennel change its iron content?
Boiling can slightly reduce the iron content per 100 g because some minerals dissolve into the cooking water, especially when the water is poured off afterward. Steaming and roasting keep more nutrients in the bulb. The calculator's boiled preset of 0.66 mg/100 g is a reasonable estimate for drained, cooked fennel.