Crude Protein Calculator
Enter the nitrogen percentage from a lab analysis and a nitrogen-to-protein conversion factor. The default factor of 6.25 is a common convention, not a universal constant, so use the factor appropriate to your sample type if you know it.
Last updated: September 26, 2026
Frequently asked questions
What is crude protein?
Crude protein is an estimate of protein content calculated from the total nitrogen measured in a sample, using a conversion factor, rather than measuring protein molecules directly.
Why 6.25 as a default factor?
Typical proteins are assumed to be about 16% nitrogen by mass, and 1 / 0.16 = 6.25. It's a widely used convention, not a measured constant for every material.
Why might I need a different factor?
Different foods and feeds have different average nitrogen content in their proteins. Some standards specify other factors for specific commodities. Use the factor that matches your material and analytical standard if you know it.
Can crude protein be higher than the true protein content?
Yes. Nonprotein nitrogen sources, such as urea, nitrates, or free amino acids, add to the measured nitrogen without being protein, so crude protein can overestimate actual protein.
What if the result is above 100%?
That is not physically possible for the sample as a whole, so the calculator flags it. Check whether the nitrogen percentage and conversion factor you entered actually apply to your sample.
How is this different from Protein Concentration?
Protein Concentration on this site calculates protein amount in a liquid solution, often from absorbance. This calculator estimates a solid or feed sample's protein percentage from its nitrogen content.