Fennel is a crisp, mildly sweet vegetable that shows up in salads, soups, roasts, and even herbal tea. Unlike starchy root vegetables, raw fennel is relatively low in carbohydrates: a 100 g portion of the bulb contains about 7.3 g of total carbs and 4.2 g of net carbs after subtracting dietary fiber.
This calculator helps anyone tracking macronutrients, managing blood sugar, or following a low-carb or keto diet quickly find the carbohydrate value of an exact serving size. Choose a portion weight, pick the fennel form, and the tool returns total carbohydrates, dietary fiber, and net carbohydrates in a clean, easy-to-read breakdown.
The calculator supports raw fennel bulb, cooked fennel bulb, and fennel seeds, with automatic ounce-to-gram conversion and quick-fill presets for common servings.
How to Use This Tool
Enter the fennel amount and choose whether you're working with raw fennel bulb, cooked fennel bulb, or whole fennel seeds. The calculator converts ounces to grams automatically, then multiplies the reference carbohydrate values by your portion size. Use the preset chips for common portions, or type any custom amount.
How the Carb Math Works
Nutrition databases list carbohydrates per 100 g of food. The calculator takes your serving weight in grams, divides it by 100 to get a multiplier, and applies that multiplier to the per-100 g values. Net carbs are total carbohydrates minus dietary fiber, because fiber is not fully absorbed by the body and has a much smaller effect on blood sugar.
Reference values used in this calculator:
| Fennel form | Total carbs / 100 g | Fiber / 100 g | Net carbs / 100 g |
|---|---|---|---|
| Raw fennel bulb | 7.3 g | 3.1 g | 4.2 g |
| Cooked / boiled fennel bulb | 6.5 g | 2.7 g | 3.8 g |
| Fennel seeds | 52.3 g | 39.8 g | 12.5 g |
These are common USDA-style averages. A packaged fennel seed product may vary, so check its nutrition label for the most accurate numbers.
Worked Examples
Example 1: 150 g raw fennel bulb
Multiplier = 150 ÷ 100 = 1.5.
Total carbs = 7.3 × 1.5 = 11.0 g.
Fiber = 3.1 × 1.5 = 4.7 g.
Net carbs = 11.0 − 4.7 = 6.3 g.
Example 2: 1 tablespoon fennel seeds (about 6 g)
Multiplier = 6 ÷ 100 = 0.06.
Total carbs = 52.3 × 0.06 = 3.1 g.
Fiber = 39.8 × 0.06 = 2.4 g.
Net carbs = 3.1 − 2.4 = 0.7 g.
This shows why a tiny portion of seeds can still fit into a low-carb eating pattern.
Common Mistakes to Avoid
- Confusing total carbs with net carbs. Track the value that matches your dietary approach; many low-carb plans use net carbs, while some food labels only show total carbs.
- Using raw weights for cooked fennel. Cooking changes water content and density; if you tracked the raw weight, use the raw values.
- Treating all fennel parts identically. The feathery fronds, the bulb, and the seeds have different nutrient densities, and the seeds are far more carb-dense by weight.
- Estimating portions by eye. A digital kitchen scale removes most of the guesswork from macro tracking.
Precision Notes
Carbohydrate values for fresh fennel can vary slightly with growing conditions, harvest time, and storage. The figures here are solid averages, not lab results for your specific batch. For the most up-to-date and complete nutrient data, search for "fennel" in the USDA FoodData Central database at fdc.nal.usda.gov. The difference between 3 g and 4 g of fiber in a large bowl is unlikely to change your daily totals dramatically, but label reading matters for processed fennel seed products.
Frequently Asked Questions
Can I eat fennel on a low-carb or keto diet? Yes. A 100 g serving of raw fennel bulb has roughly 4.2 g net carbs. A typical half-cup portion is about 44 g, so it is easy to fit into even a strict keto macro target.
Why do fennel seeds show so many more carbs than the bulb? Seeds are much drier and more calorie-dense than the water-rich bulb. They are usually eaten in tiny amounts, so the practical carb impact is often still small. A single teaspoon of seeds weighs about 3 g.
Does boiling fennel remove carbohydrates? No, cooking does not destroy carbohydrates. Boiling in water may leach a small amount of water-soluble vitamins, but the carbohydrate content stays roughly the same; the weight changes mainly reflect water loss or absorption.
Fennel is also valuable for its potassium and other minerals. If you are tracking electrolytes, the Fennel Potassium Calculator can help you estimate that intake too.