Nutrition labels across the world typically list energy and protein per 100 grams, a universal baseline that makes comparison straightforward. But most people eat serving sizes that differ from 100 g — a chicken breast might weigh 180 g, a tub of yogurt 150 g, a portion of rice 200 g. This Energy Protein Per 100g Calculator converts those label values into the numbers that actually matter on your plate: energy per serving, protein per serving, and protein’s share of the calories.
Whether you are tracking macros for muscle building, counting calories for weight loss, or simply curious about the protein density of different foods, this tool gives you instant answers. It also lets you switch between grams and ounces, adjust for multiple servings, and explore quick-start presets for common high-protein staples. No sign-up, no complex apps — just accurate scaling of the per 100 g nutrition panel to your actual portion.
🔢 Nutrition values per 100 g
📊 Your results
How to Use This Tool
Enter the energy value (in kcal) and protein value (in grams) exactly as they appear on the nutrition panel for 100 g of food. Then enter the amount you plan to eat — either in grams or ounces using the dropdown — and the number of servings. Press Calculate and the tool scales everything to your portion.
- Leave the amount field in grams for most European, UK and Australian labels; switch to ounces if you are using a US recipe or kitchen scale.
- For packaged foods with a serving size on the label, enter that serving size directly, or multiply your portion by the number of servings.
- Use the quick-pick buttons (chicken breast, Greek yogurt, lentils, salmon, egg) as a starting point, then adjust values to match the exact product.
The result panel shows total portion weight, energy per serving, protein per serving, energy density per gram, calories from protein, and protein share of total energy. The last row also tells you how many grams of protein you get per 100 kcal — a handy indicator of protein density when comparing foods. Need to plan an entire meal? Try the protein per cup calculator for volumetric portion sizes.
The Math Behind It
The calculation is a proportional scaling problem:
Energy per serving = (Energy per 100 g / 100) × portion weight in grams × number of servings
Protein per serving = (Protein per 100 g / 100) × portion weight in grams × number of servings
If the portion is entered in ounces, it is first converted to grams using the factor 1 oz = 28.3495 g. Protein contributes 4 kcal per gram, so the calories from protein are simply protein grams × 4. Dividing that by the total energy per serving and multiplying by 100 gives the percentage of energy coming from protein.
For example, if a food provides 10 g protein and 200 kcal per 100 g, the protein density is (10 × 4) / 200 × 100 = 20% of calories from protein.
Worked Examples
Example 1: Chicken breast — 100 g of cooked chicken breast has about 165 kcal and 31 g protein. If you eat a 180 g fillet, the tool calculates 165/100 × 180 = 297 kcal and 31/100 × 180 = 55.8 g protein. The calories from protein are 55.8 × 4 = 223 kcal, which is 75% of the total energy.
180 g cooked chicken breast: ≈ 297 kcal, 56 g protein, ~75% of calories from protein.
Example 2: Greek yogurt — Plain non-fat Greek yogurt is roughly 59 kcal and 10 g protein per 100 g. A 150 g pot supplies 59/100 × 150 = 88.5 kcal and 15 g protein. Protein makes up 60 of those 88.5 kcal, or about 68%.
Example 3: Lentils — Cooked lentils have about 116 kcal and 9 g protein per 100 g. A 200 g serving delivers 232 kcal and 18 g protein, with only 31% of calories from protein. This shows why legumes, while protein-rich, are also carbohydrate-rich — check the beans nutrition calculator for a breakdown.
Tips & Best Practices
- Use drained or cooked weights for accuracy. The per-100g value on dried pasta or rice applies to the uncooked product; cooked weights absorb water and change the density.
- Double-check whether the label refers to raw or cooked meat. Raw and cooked chicken differ in water content, so per-100g values are not interchangeable.
- Weigh foods with a digital kitchen scale whenever possible. Volume-based estimates (cups, spoons) are far less precise for protein-dense foods.
- Remember that the 4 kcal rule for protein is a general Atwater factor; some proteins yield slightly different metabolizable energy, but 4 kcal/g is the standard used on nutrition labels.
- Compare foods using protein per 100 kcal rather than protein per 100 g — it reveals which food delivers more protein for fewer calories.
If you are eating a large portion, don’t forget to set the “Servings” field. Many people enter a single serving weight but unknowingly eat two or three.
Reference Data: Approximate per-100g Values
These values are typical cooked, edible portions from USDA FoodData Central. Actual products vary by brand and preparation method.
| Food | kcal / 100 g | Protein / 100 g | % kcal from protein |
|---|---|---|---|
| Chicken breast, cooked | 165 | 31 | 75% |
| Salmon, cooked | 208 | 20 | 38% |
| Egg, whole, cooked | 155 | 13 | 34% |
| Greek yogurt, non-fat | 59 | 10 | 68% |
| Lentils, cooked | 116 | 9 | 31% |
| Tofu, firm | 76 | 8 | 42% |
| Brown rice, cooked | 123 | 2.7 | 9% |
Use the tool to verify any of these numbers, or replace them with values from the official USDA FoodData Central searchable database.
Frequently Asked Questions
Why are protein amounts shown as “per 100 g” on European labels? The EU Food Information Regulation requires nutrition declarations per 100 g or 100 ml so consumers can compare products directly, regardless of package size.
Is more protein per 100 g always better? Not necessarily. Protein density (grams per 100 kcal) and the quality of the amino acid profile also matter. Lean meats and low-fat dairy usually score highly on both.
Does cooking change the protein content? Cooking can change the weight through moisture loss, but the absolute protein content stays roughly the same. That is why per-100g values differ between raw and cooked meats — the denominator changes, not the protein.
Can this calculator help with weight loss? Yes. High-protein foods increase satiety and help preserve lean mass during a calorie deficit. The percentage of energy from protein and the protein density row make it easy to choose filling, protein-rich options within a calorie budget.
For more context on energy balance, see the WHO healthy diet fact sheet or the NHS Eat Well guide.