Tracking fruit by the slice is one of the easiest ways to keep portions honest without weighing an entire bag of produce. This calculator turns a simple count of slices into a reliable calorie estimate using the calorie density of 12 common fruits — from apples and bananas to watermelon and kiwi.
Enter the fruit, the average weight of one slice, and how many slices you plan to eat. The tool immediately returns calories per slice, total calories for your serving, and the carbohydrates, protein, and fat that come with it. It's ideal for meal prep, diet planning, and anyone who likes a visual portion cue instead of a measuring cup.
You can use the handy thin/medium/thick quick-set buttons for typical slice weights, or switch between grams and ounces if you prefer kitchen-scale units. Since water-rich fruits like watermelon and cantaloupe are much lighter per slice than bananas or mangoes, using a real weight makes a big difference.
🥝 1. Choose your fruit
2. Set your slice size
🍽️ 3. Number of slices
How to Use This Tool
This calculator is designed for anyone who portions fruit by sight rather than by weighing a whole batch. Start by selecting your fruit from the dropdown — the list covers 12 common choices with calorie values from standard food-composition databases. Next, choose a slice size. The thin/medium/thick buttons insert typical weights (40 g, 55 g, and 85 g), or you can type a custom gram or ounce weight if your slices are larger or smaller. Finally, enter the number of slices you plan to eat and press Calculate.
The results panel shows the calories in a single slice, the total for your full serving, and a macronutrient breakdown for the whole portion. A short calculation line also reveals the math behind the number, so you can see exactly why a dense banana slice costs more calories than a watermelon slice of the same size.
- Use the reset button to clear all fields and start a new fruit.
- Switch the unit dropdown to ounces if your recipes use imperial measurements.
- The calculator works for whole, fresh fruit — not dried, candied, or juice-packed fruit.
How the Calculation Works
Every fruit has a calorie density — the number of kilocalories in 100 grams of edible flesh. The calculator applies that density to the total weight of your serving:
Total weight = slice weight × number of slices
For example, a standard medium apple has about 52 kcal per 100 g. If one slice weighs 55 g, the slice contains 55 × 52 ÷ 100 = 28.6 kcal. Eat three slices, and you add roughly 85.8 kcal. The same logic applies to carbohydrates (13.8 g per 100 g in apples), protein, and fat.
Because the calculation is based on weight, water content matters enormously. Watermelon and cantaloupe are over 90% water, so they have only 30–34 kcal per 100 g. Bananas and grapes are starch- and sugar-dense, landing at 69–89 kcal per 100 g. A thick slice of a dense fruit can easily contain two to three times the calories of a thick slice of a watery fruit.
Worked Examples
Example 1: Apple snack. You cut a medium apple into 4 slices; each slice weighs about 55 g. Enter apple, 55 g per slice, 3 slices. Total weight = 165 g. Calories = 165 × 52 ÷ 100 = 85.8 kcal. Carbohydrates = 165 × 13.8 ÷ 100 = 22.8 g.
Example 2: Watermelon at a cookout. Thick wedges often weigh 85 g per slice. Enter watermelon, 85 g, 2 slices. Total weight = 170 g. Calories = 170 × 30 ÷ 100 = 51 kcal. That's a low-calorie, hydrating snack — but watch out for the serving size if you go back for thirds.
Example 3: Banana on cereal. A half-inch banana slice is roughly 25 g. Enter banana, 25 g, 6 slices. Total weight = 150 g. Calories = 150 × 89 ÷ 100 = 133.5 kcal. This shows why banana slices can sneak into a breakfast bowl faster than you expect.
Reference Data: Calories in Common Sliced Fruits
The table below shows the calorie density of each fruit in this calculator, plus the calories in a 40 g and a 60 g slice. Use these as a quick reference when you don't have the calculator open.
| Fruit | kcal / 100 g | 40 g slice | 60 g slice |
|---|---|---|---|
| Apple | 52 | 20.8 | 31.2 |
| Banana | 89 | 35.6 | 53.4 |
| Orange | 49 | 19.6 | 29.4 |
| Watermelon | 30 | 12 | 18 |
| Strawberries | 32 | 12.8 | 19.2 |
| Pineapple | 50 | 20 | 30 |
| Mango | 60 | 24 | 36 |
| Grapes | 69 | 27.6 | 41.4 |
| Peach | 39 | 15.6 | 23.4 |
| Pear | 57 | 22.8 | 34.2 |
| Kiwi | 61 | 24.4 | 36.6 |
| Cantaloupe | 34 | 13.6 | 20.4 |
Values are based on raw, edible portion without peel where peel is usually discarded. Always weigh your own portions for medical or competition-level accuracy.
Tips for Accurate Tracking
- Invest in a digital kitchen scale and weigh in grams. Volume-based slices are inconsistent.
- Trim the rind, core, stem, and seeds before weighing the edible part you actually eat.
- For berries, measure by weight rather than by cup; a cup can vary by 20–40 g depending on how tightly it's packed.
- If you're tracking macros, remember the carbs in fruit are mostly natural sugars and fiber. The fiber content delays blood sugar spikes but still counts toward total carbs.
- Pre-slice and store fruit in clear containers so grab-and-go portions match your logged serving.
Frequently Asked Questions
Are the calorie values exact? No. USDA food-composition values are averages of many samples. Fruit sweetness, variety, ripeness, and growing conditions can shift calories by 5–10% in either direction.
Does slicing fruit change its calories? Slicing does not change the energy content — the same grams of fruit have the same calories whether whole, sliced, or pureed. However, slicing can change how much you eat, because smaller pieces fill a bowl more and are easier to over-serve.
Why did my apple slice weigh more than the preset? Preset slice weights are just general ranges. A large Honeycrisp can easily produce 90 g slices, while a small gala gives 35–45 g slices. Use the custom weight field for real accuracy.
Should I count fruit calories at all? For many people, fruit is a health food and not the main driver of excess calories. But if you're following a strict calorie target, weighing fruit is still worthwhile because several servings can add up to 200–300 kcal. For blood-sugar considerations, pair this tool with the fruit glycemic load calculator.
What about strawberries as individual slices? Strawberries are usually counted by the berry or by weight. A per-gram approach can be handy, and the strawberry calories per gram calculator gives you that level of detail.