Crude Protein Calculator
Calculate crude protein content from nitrogen analysis. Crude protein is estimated using the Kjeldahl method: Protein (%) = Nitrogen (%) × 6.25. Commonly used in animal feed analysis, food testing, and agricultural labs.
Formula
Crude Protein (%) = Nitrogen (%) × 6.25
Protein mass = Sample weight × [Nitrogen (%) / 100] × 6.25
- The factor 6.25 converts nitrogen to protein: (100 / 16) = 6.25, assuming proteins are ~16% nitrogen
- Applies to most plant-based foods and animal feeds
- For dairy products, use 6.38; for soy, use 5.71 for more accuracy
- Kjeldahl method measures total nitrogen, not just protein nitrogen (may include non-protein N)
- Crude protein ≥ true protein (especially if non-protein nitrogen present)
Crude Protein Calculation Example
Inputs
- Nitrogen Content: 2.5 %
- Sample Weight: 100 g
A 100g feed sample contains 2.5% nitrogen. Crude Protein = 2.5 × 6.25 = 15.625%. Total crude protein = 100g × 15.625% = 15.625g.
Frequently asked questions
What is crude protein?
Crude protein is an estimate of total protein calculated from nitrogen content using the Kjeldahl method and conversion factor 6.25, commonly used in feed and food analysis.
Why multiply nitrogen by 6.25?
Proteins average ~16% nitrogen by mass, so 100/16 = 6.25 converts nitrogen percentage to protein percentage.
Is crude protein the same as true protein?
No. Crude protein includes all nitrogen (including non-protein nitrogen like nitrates), while true protein is only actual protein amino acids.
When is crude protein used?
Animal feed labeling, food testing, agricultural analysis, and nutritional assessment where approximate protein content is needed.
What is the Kjeldahl method?
Kjeldahl is a laboratory technique to measure total nitrogen in a sample by chemical digestion and titration, forming the basis for crude protein calculations.