Crude Protein Calculator

Nitrogen to Protein Conversion for Food & Feed

Calculate crude protein content from nitrogen analysis. Enter nitrogen percentage or mass, sample mass, and conversion factor to get protein content in percent and grams.

Example Calculations

Try these sample calculations to see how the calculator works.

Feed Sample (Kjeldahl Method)

Feed

A 10 g feed sample contains 0.24 g nitrogen. Calculate crude protein using the default factor.

Sample Mass (g): 10 g

Nitrogen Mass (g): 0.24 g

Nitrogen (%): %

Conversion Factor: 6.25

Wheat Flour (Custom Factor)

Wheat

A wheat flour sample has 2.1% nitrogen. Use a conversion factor of 5.7.

Sample Mass (g): g

Nitrogen Mass (g): g

Nitrogen (%): 2.1 %

Conversion Factor: 5.7

Milk Protein Calculation

Milk

A 20 g milk sample contains 0.22 g nitrogen. Use a conversion factor of 6.38.

Sample Mass (g): 20 g

Nitrogen Mass (g): 0.22 g

Nitrogen (%): %

Conversion Factor: 6.38

Egg White (Direct Percentage)

Egg

Egg white contains 2.0% nitrogen. Use the default conversion factor.

Sample Mass (g): g

Nitrogen Mass (g): g

Nitrogen (%): 2.0 %

Conversion Factor: 6.25

Other Titles
Understanding Crude Protein Calculator: A Comprehensive Guide
Master nitrogen-to-protein conversion for food, feed, and agricultural analysis.

What is Crude Protein?

  • Definition and Importance
  • Nitrogen Content in Protein
  • Common Conversion Factors
Crude protein is an estimate of total protein content in a sample, calculated from its nitrogen content. It is widely used in food and feed analysis, especially in agriculture and animal nutrition.
Why Nitrogen?
Proteins are made up of amino acids, which contain nitrogen. By measuring nitrogen, we can estimate protein content using a conversion factor.
Conversion Factors
The most common factor is 6.25, but others are used for specific foods (e.g., 5.7 for wheat, 6.38 for milk).

Crude Protein Examples

  • Feed sample: 2.4% N × 6.25 = 15% crude protein.
  • Wheat flour: 2.1% N × 5.7 = 11.97% crude protein.

Step-by-Step Guide to Using the Crude Protein Calculator

  • Input Nitrogen Data
  • Choose Conversion Factor
  • Interpret Results
Enter either nitrogen mass and sample mass, or nitrogen percentage. Select the appropriate conversion factor for your sample type.
Automatic Calculations
If you enter nitrogen mass and sample mass, the calculator will compute nitrogen percentage for you.
Result Interpretation
Results include crude protein percentage and total protein mass in grams.

Usage Examples

  • 10 g sample, 0.24 g N, factor 6.25 → 15% protein, 1.5 g protein.
  • 2.1% N, factor 5.7 → 11.97% protein.

Real-World Applications of Crude Protein Calculation

  • Feed and Food Quality Control
  • Agricultural Research
  • Nutritional Labeling
Crude protein analysis is essential for animal feed formulation, food quality control, and agricultural research. It helps ensure nutritional adequacy and regulatory compliance.
Feed Industry
Feed manufacturers use crude protein values to balance animal diets and optimize growth.
Food Industry
Food scientists use protein content for labeling and quality assurance.

Application Examples

  • Dairy feed: 16% crude protein required for optimal milk yield.
  • Bread flour: protein content affects baking quality.

Common Misconceptions and Correct Methods

  • Crude vs. True Protein
  • Conversion Factor Selection
  • Calculation Pitfalls
Crude protein is not the same as true protein. It may overestimate protein if non-protein nitrogen is present. Always use the correct conversion factor for your sample type.
Non-Protein Nitrogen
Some feeds contain urea or other non-protein nitrogen sources, which can inflate crude protein values.
Calculation Errors
Ensure all units are correct and inputs are accurate to avoid errors.

Misconception Examples

  • Urea in feed increases crude protein but not true protein.
  • Using 6.25 for wheat underestimates true protein.

Mathematical Derivation and Examples

  • Nitrogen to Protein Formula
  • Worked Calculation Examples
  • Unit Conversions
Crude protein (%) = Nitrogen (%) × Conversion Factor. If you have nitrogen mass and sample mass: Nitrogen (%) = (N mass / sample mass) × 100.
Example Calculation
A 10 g sample with 0.24 g N: (0.24 / 10) × 100 = 2.4% N. Crude protein = 2.4 × 6.25 = 15%. Protein mass = 10 × 0.15 = 1.5 g.
Direct Percentage
If you have nitrogen percentage, simply multiply by the factor to get crude protein percentage.

Calculation Examples

  • Milk: 0.22 g N in 20 g, factor 6.38 → 7.01% protein, 1.4 g protein.
  • Egg white: 2.0% N × 6.25 = 12.5% protein.