A half-cup serving of cooked black beans contains about 12 grams of net carbs. That’s based on roughly 20 grams of total carbohydrates minus 8 grams of fiber. A full cup bumps that up to around 26 grams of net carbs (40.8 grams total carbs minus 15 grams of fiber).
How Net Carbs Are Calculated
Net carbs equal total carbohydrates minus fiber. Your body can’t fully digest fiber, so it doesn’t raise blood sugar the way starches and sugars do. Black beans are notably high in fiber, which is why their net carb count is significantly lower than their total carb number. Of the roughly 7 grams of fiber in a half-cup serving, about 2.8 grams are soluble fiber, the type that slows digestion and helps regulate blood sugar. The rest is insoluble fiber, which supports digestive health.
Black Beans and Blood Sugar
Despite having a moderate amount of net carbs, black beans have a glycemic index of about 30, which is considered low. Foods below 55 on the GI scale release glucose slowly, and black beans sit well below that threshold. This means the carbs in black beans don’t hit your bloodstream all at once.
Part of the reason is resistant starch, a type of starch that behaves more like fiber. Cooked black beans contain about 5% resistant starch by dry weight. If you cook black beans and then refrigerate them for up to 24 hours, that number rises to 5–6% as some of the starch molecules recrystallize. So cold black bean salads or reheated leftovers may have a slightly lower effective carb impact than freshly cooked beans.
Can Black Beans Fit a Low-Carb Diet?
That depends on how strict your carb limit is. Most people following a keto diet aim for 25 grams of net carbs or fewer per day. A single half-cup of black beans uses up almost half that budget at 12 grams, leaving very little room for anything else. It’s technically possible to include them, but you’d need to plan the rest of your day carefully.
If your daily target is closer to 50 grams of net carbs, which is common for less strict low-carb approaches, a half-cup serving fits comfortably. You’d still have 38 grams to work with for the rest of the day. The key is sticking to that half-cup portion, since a full cup nearly doubles the count.
How Black Beans Compare to Other Legumes
All legumes are relatively high in carbs, but fiber content varies enough to create meaningful differences in net carbs. Here’s how common legumes compare per one-cup cooked serving:
- Soybeans: 4.1 g net carbs (14.4 g carbs, 10.3 g fiber)
- Peas: 16.2 g net carbs (25 g carbs, 8.8 g fiber)
- Lentils: 24.2 g net carbs (39.8 g carbs, 15.6 g fiber)
- Black beans: 25.8 g net carbs (40.8 g carbs, 15 g fiber)
- Kidney beans: 27.3 g net carbs (40.4 g carbs, 13.1 g fiber)
- Navy beans: 28.2 g net carbs (47.3 g carbs, 19.1 g fiber)
- Pinto beans: 29.4 g net carbs (44.8 g carbs, 15.4 g fiber)
- Chickpeas: 32.5 g net carbs (45 g carbs, 12.5 g fiber)
Black beans land in the middle of the pack. If you’re looking for the lowest-carb legume option, soybeans (including edamame) are in a class of their own at just 4 grams of net carbs per cup. Lentils are nearly identical to black beans. Chickpeas and pinto beans sit at the higher end.
Canned vs. Dried Black Beans
The net carb count is essentially the same whether you cook dried black beans yourself or open a can. The main difference with canned beans is sodium, not carbs. Some canned varieties add sugar or other ingredients, so checking the nutrition label is worth the few seconds it takes. Draining and rinsing canned black beans removes a portion of the sodium but doesn’t change the carbohydrate content in any meaningful way.
Practical Portions
A half cup of cooked black beans is smaller than most people expect. It’s roughly the size of a cupped handful, or about the amount you’d get in a typical side dish at a restaurant. If you’re adding black beans to a burrito bowl or soup, you’re likely using closer to a full cup, which puts you at 26 grams of net carbs from the beans alone. Measuring once or twice with an actual measuring cup can help you calibrate your eye so you know what a half-cup portion looks like on your plate.