How many calories are in one gram of protein?
Protein supplies about 4 calories per gram under the general energy factor used on nutrition labels. Multiply protein grams by 4 to estimate calories supplied by protein.
Free bidirectional converter
SMALL CONVERSION. CLEARER NUTRITION.Protein to Calorie Calculator
Convert protein grams to calories—or calories from protein back to grams. The general nutrition-label factor is 4 calories per gram of protein.
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Everyday food. A little more clarity.
The simple conversion25 g protein.
100 calories from protein.
100 calories from protein.
Grams ↔ calories
4 kcal per gram
Quick protein presets
Food-label context
YOUR PROTEIN, IN ANOTHER UNIT
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4 kcal per gram
Protein grams and calorie converter
Convert protein itself—not the total calories in a food.
g
Result
100 kcal
25 g × 4 kcal/g
Important: this result is the energy supplied by protein only. A food with 25 g protein may contain more than 100 calories because fat, carbohydrate, alcohol, fiber, and label rounding can affect its total.
The two formulas
Protein grams → calories
grams × 4 = kcal
Protein calories → grams
kcal ÷ 4 = grams
Quick answer: 100g protein
400 calories
This refers to 100 grams of pure protein as a nutrient. It does not mean 100 grams of chicken, tofu, yogurt, beans, or protein powder contains 400 calories.
Protein grams to calories chart
These are protein-derived calories. Use a food's Nutrition Facts label for its total calories.
Scroll to compare all columns
| Protein | Calories from protein | Calculation |
|---|---|---|
| 10 g | 40 kcal | 10 × 4 |
| 20 g | 80 kcal | 20 × 4 |
| 25 g | 100 kcal | 25 × 4 |
| 30 g | 120 kcal | 30 × 4 |
| 40 g | 160 kcal | 40 × 4 |
| 50 g | 200 kcal | 50 × 4 |
| 75 g | 300 kcal | 75 × 4 |
| 100 g | 400 kcal | 100 × 4 |
KNOW WHAT THE NUMBER MEANS
Protein calories vs total food calories
Keep the protein calculation and the whole food in view.
Protein calories
Only the energy attributable to protein grams. Example: 25 g protein contributes about 100 kcal.
Total food calories
Includes protein plus carbohydrate, fat, alcohol when present, and the effects of label-calculation rules.
What to track
Use the package label or USDA food entry for a food's total calories; use this tool only for protein-unit math.
Example: a shake with 25 g protein has at least about 100 calories from protein. If it also contains 10 g carbohydrate and 3 g fat, those nutrients add energy, so the shake's total will be higher. Always treat the product label as the source of truth.
Which calculator should you use?
Frequently asked questions
How many calories are in 100 grams of protein?
One hundred grams of protein supplies about 400 calories. This means 100 grams of the nutrient protein—not 100 grams of a protein-containing food.
How many calories are in 25 grams of protein?
Twenty-five grams of protein supplies about 100 calories because 25 multiplied by 4 equals 100.
Why does my protein food have more calories than this calculator shows?
The calculator counts only calories supplied by protein. Foods and shakes may also contain carbohydrate and fat, and nutrition labels use permitted rounding, so total calories can be higher.
Can I use this calculator to set my daily protein target?
No. This converter changes units only. Use the daily Protein Calculator for a goal-based protein range, or the Macro Calculator for protein, carbohydrate, fat, and total calorie targets.
THE REFERENCES BEHIND THE CONVERSION
Sources reviewed
- Protein: Interactive Nutrition Facts Label - U.S. Food and Drug Administration
- The New Nutrition Facts Label - U.S. Food and Drug Administration
- FoodData Central - U.S. Department of Agriculture
This calculator performs general nutrition-label unit conversion. It does not estimate digestion, individual energy use, food-specific calories, or a personal protein target.