Fennel is a crisp, mildly anise-flavored vegetable that's often overlooked as a source of electrolytes. Raw fennel bulb is surprisingly rich in potassium — roughly 414 mg per 100 g, which is comparable to a medium banana. This calculator converts any serving size you actually measure — grams, ounces, cups of sliced fennel, or whole bulbs — into milligrams of potassium and a percentage of your daily target.
Whether you're tracking potassium for general nutrition, managing blood pressure, or balancing electrolytes around exercise, this tool gives you a fast estimate. You can also set a custom daily potassium target (the default is the FDA's 4,700 mg guideline) to see how close a serving gets you to your goal. The result panel also shows a banana equivalent, the total weight of your serving, and how much fennel would be needed to meet your entire target — handy for meal planning and grocery decisions.
🥗 Serving Details
📊 Your Potassium Breakdown
Quick Start
Start by entering how much fennel you plan to eat. If you have a kitchen scale, enter the weight in grams for the most accurate result. No scale? Select ounces, cups of sliced fennel, or whole medium bulbs from the unit dropdown, and the calculator converts the volume or piece count using typical trimmed fennel weights.
Next, set your daily potassium target. The default is 4,700 mg, the Adequate Intake used by the FDA for adults. This makes the percent daily value easy to interpret. Click Calculate, and the result panel shows the potassium in mg, the percent of your target, the converted serving weight, a banana equivalent, and how much fennel would be needed to reach 100% of your target.
The Math Behind It
The calculator applies a single conversion factor from the USDA FoodData Central nutrient database: raw fennel bulb contains about 414 mg of potassium per 100 g of edible portion. Dividing by 100 gives 4.14 mg of potassium per gram of raw fennel bulb.
Potassium (mg) = fennel weight in grams × 4.14
Percent of target = potassium ÷ daily target × 100
For a unit like a cup or a medium bulb, the calculator first converts to grams using the typical weights shown in the reference table below, then applies the same formula. The banana equivalent is simply your potassium total divided by 422 mg, the approximate potassium content of a medium banana.
Worked Example
Suppose you slice one cup of raw fennel bulb and want to know what it contributes to a 4,700 mg daily target.
Serving: 1 cup sliced fennel ≈ 87 g
Potassium = 87 × 4.14 = 360 mg
Percent of 4,700 mg target = 360 ÷ 4,700 × 100 = 7.7%
If you eat a whole medium bulb instead, roughly 234 g, the calculator would show about 969 mg of potassium, or 21% of a 4,700 mg target. That is more than two medium bananas' worth of potassium in one vegetable serving.
Unit Reference
The following weights are typical for raw fennel bulb. Individual bulbs vary by size and variety, so treat piece-based units as estimates.
| Unit | Approx. weight | Potassium |
|---|---|---|
| 1 gram | 1 g | 4.14 mg |
| 1 ounce | 28.35 g | 117 mg |
| 100 grams | 100 g | 414 mg |
| 1 cup sliced | 87 g | 360 mg |
| 1 medium bulb | 234 g | 969 mg |
If you need more precise numbers, check the product label or search the USDA FoodData Central database for raw fennel bulb.
Tips & Best Practices
- Use a digital kitchen scale when potassium accuracy matters, such as following a doctor-recommended potassium target. Volume estimates can be off by 10–15%.
- If you boil fennel, some potassium dissolves into the cooking water. The raw values here will overestimate boiled fennel; for drained boiled fennel, look up a cooked entry or account for the loss.
- Slice fennel fresh rather than letting it sit in water before serving. Soaking in water can also leach water-soluble minerals.
- Celebrate the bulb rather than the stalks and fronds when tracking potassium. The bulb is the part covered by this calculator.
- For meal planning, combine this with the Fennel Carb Calculator if you also track net carbohydrates.
Limitations & Precision Notes
The 414 mg per 100 g value comes from a generic USDA entry for raw fennel bulb. Actual potassium can vary with growing conditions, soil potassium levels, variety, harvest time, and how the fennel was stored. A difference of 10–20 mg per 100 g is normal and rarely changes the practical interpretation of a serving.
Cooking method matters: boiling and blanching reduce potassium because the mineral moves into the water. Roasting and sautéing cause some moisture loss, which can slightly concentrate potassium per gram. For medical conditions that require strict potassium limits, use laboratory-backed nutrition data and consult a registered dietitian or physician. The NIH Potassium fact sheet is a good starting point for evidence-based potassium recommendations.
Frequently Asked Questions
Is fennel a good source of potassium? Yes. A 100 g serving of raw fennel bulb provides about 414 mg, which is nearly 9% of the 4,700 mg Adequate Intake. That is comparable to a medium banana.
Can I use this calculator for fennel seeds or fennel tea? No. This calculator is for raw fennel bulb only. Fennel seeds are a different food with a different nutrient density, and brewed tea contains very little potassium per cup.
How does fennel compare with other potassium-rich produce? It is competitive with many fruits and vegetables. A medium banana has about 422 mg, one cup of sliced fennel has about 360 mg, and 100 g of raw mango provides around 168 mg. Compare with the Mango Potassium Calculator to see other produce options.
What if my daily target is not 4,700 mg? Enter your own target in the calculator. People with kidney disease, hypertension, or specific medication regimens often have a different recommended potassium limit, so check with your healthcare provider.