Choy — bok choy, Shanghai bok choy, and napa cabbage — is one of the most low-calorie leafy vegetables you can put on a plate. But because packaged nutrition labels rarely list per-slice figures, it's easy to guess wrong when you're counting calories. This calculator turns the weight of your chopped batch and the number of slices into a reliable per-slice calorie estimate, along with carbs, protein, fat, and fiber.
Meal preppers, weight-loss trackers, and anyone building a balanced diet can use it to portion bok choy accurately without weighing every individual leaf. Just select the choy variety, enter the total sliced weight and slice count, and the tool does the rest.
You can also add an optional serving size to see calories per serving, or use the preset buttons for common portions like one cup or one small head.
How to Use This Tool
Select the choy variety from the dropdown. Raw bok choy and baby bok choy both contain about 13 kcal per 100 g, while napa cabbage is slightly lower at about 12 kcal per 100 g. After that, weigh the whole batch once it has been washed, trimmed, and sliced. If you use a kitchen scale, place a bowl on the scale and zero it before adding the leaves so the weight reflects only the choy.
Enter that weight in the first field, then choose grams, kilograms, or ounces from the small unit selector beside it. Next, count the total number of slices in the batch. If you cut a head into 12 pieces, enter 12; this count is the denominator for all per-slice results, so it matters more than the shape of the cuts. Optionally, enter a serving size — for example, 4 slices per person — to display a serving-level calorie value. Press the Calculate button to see calories per slice, total batch calories, and the per-slice macro nutrients. The preset buttons can quickly fill in common portion weights such as one cup or one small head.
Formula Explained
Nutrition databases report choy calories per 100 g of raw vegetable, not per slice. The tool therefore converts your batch to grams first, then applies the same ratio used for any food label calculation:
Total batch calories = (batch weight in grams ÷ 100) × calories per 100 g
Calories per slice = total batch calories ÷ number of slices
Carbohydrates, protein, fat, and fiber follow the same pattern: each nutrient value per 100 g is multiplied by the batch weight fraction and then divided by the slice count. Slicing does not change the nutrient density of the vegetable, so every slice drawn from a well-mixed batch represents an equal share of the total energy.
Worked Examples
Example A. A 200 g head of bok choy is sliced into 10 pieces. Total batch calories = (200 ÷ 100) × 13 = 26 kcal. Calories per slice = 26 ÷ 10 = 2.6 kcal. If a typical serving is 5 slices, that serving contains about 13 kcal.
Example B. A 150 g head of napa cabbage is cut into 8 thick slices. Total batch calories = (150 ÷ 100) × 12 = 18 kcal. Per slice = 2.25 kcal. The macros per slice are roughly 0.41 g carbs, 0.21 g protein, 0.04 g fat, and 0.19 g fiber.
Reference Data
The default values in this calculator are based on common raw entries in the USDA FoodData Central database for leafy brassica vegetables. Real-world produce can vary with variety, harvest season, and water content, but these figures are reliable for day-to-day tracking.
| Variety | kcal per 100 g | Carbs (g) | Protein (g) | Fat (g) | Fiber (g) |
|---|---|---|---|---|---|
| Bok choy (pak choi), raw | 13 | 2.18 | 1.50 | 0.20 | 1.00 |
| Baby bok choy, raw | 13 | 2.18 | 1.50 | 0.20 | 1.00 |
| Napa cabbage, raw | 12 | 2.20 | 1.10 | 0.20 | 1.00 |
| Shanghai bok choy, raw | 13 | 2.18 | 1.50 | 0.20 | 1.00 |
Common Mistakes to Avoid
Mixing raw and cooked weights. Cooking choy in water changes its weight because water is absorbed or released, but the calorie content in the raw ingredient stays the same. Decide once whether you will weigh raw or cooked and stick with that method.
Including the root or damaged leaves. Trim the root end and discard yellow or bruised outer leaves before weighing. One large root and stem base can add several grams that never end up on your plate.
Pro tip: Slice the choy into fairly uniform pieces before counting. If you have 8 thick stalks and 12 thin leaves in the same batch, the per-slice calorie values will be less accurate. For best results, use the same slice width for the entire batch.
Frequently Asked Questions
Q: Is bok choy good for weight loss?
A: Yes. A 100 g serving of raw bok choy provides only about 13 kcal while contributing water, fiber, and several micronutrients, so it can help fill the plate without pushing your energy budget. Just remember to track any cooking oil, sauce, or dressing added to the pan, since those add calories far faster than the choy itself.
Q: How many calories are in one slice of bok choy?
A: It depends on the size. A thin slice from a small head may weigh only 5 g and contain roughly 0.7 kcal, while a thick wedge from a large head can weigh 20 g and contain about 2.6 kcal. The most accurate way to find your own slice value is to weigh the batch and divide by the number of slices, which is exactly what this tool does.
Q: Does cooked choy have the same calories per 100 g?
A: Not exactly. Boiled and drained choy has a slightly lower calorie density per 100 g because it absorbs water, but the total calories in the whole batch remain almost unchanged. If you track by weight, use the same state of preparation consistently: raw weight with raw values, cooked weight with cooked values.
Q: Can I use this for other vegetables?
A: The math works for any leafy green with known per-100 g nutrition facts. If you also track kale, the kale calories per serving calculator gives the same kind of serving-level estimate for a different vegetable.