Crude Protein Calculator

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Calculate crude protein content from measured nitrogen content.

Protein Analysis

Nitrogen Content

Conversion Factor

Quick Select

Jones Factor

Protein Results

Enter nitrogen content to see results

About this calculator

Overview

Crude protein estimation is a fundamental analytical technique in food science and nutrition that calculates protein content by measuring total nitrogen and applying a conversion factor. The method assumes that protein contains approximately 16% nitrogen by weight, though this varies by protein source. While not a direct measure of true protein content, crude protein analysis provides a standardized, cost-effective approach for nutritional labeling, feed formulation, and quality control. Modern methods like Kjeldahl digestion and Dumas combustion offer high accuracy and automation for routine analysis.

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Pro Tips

Use the default 6.25 factor for general food items or unknown mixed samples.
If you know the specific food type, adjust the Jones factor for better accuracy.
Ensure your nitrogen content is entered as a percentage (%) by mass.

Fun Facts

"The term 'crude' reflects that the measurement includes nitrogen from non-protein sources like nucleic acids, free amino acids, nucleotides, and urea."
"The standard 6.25 Jones factor is based on the assumption that proteins contain approximately 16% nitrogen (100% ÷ 16% = 6.25)."
"Food-specific factors are more accurate: dairy products use 6.38, wheat uses 5.70, corn uses 5.68, and edible insects require 5.33."
"The 6.25 factor often overestimates true protein content by 15-20% because it includes non-protein nitrogen sources."
"Kjeldahl method (1883) revolutionized protein analysis by enabling quantitative nitrogen determination through acid digestion."
"Dumas method (1831) provides faster, automated analysis without hazardous chemicals, increasingly preferred in modern laboratories."
"In 2026, automated nitrogen analyzers can process hundreds of samples daily with precision better than 0.1%."
"Protein quality assessment requires additional tests beyond crude protein, such as amino acid profiling and digestibility studies."
"The 2008 melamine scandal highlighted the flaw in crude protein testing: melamine (66% nitrogen) was added to milk to artificially boost protein readings."
"Non-protein nitrogen (NPN) can also come from urea, which is sometimes added to cattle feed as a cheap nitrogen source for rumen bacteria."

Formula: Crude Protein (%) = Nitrogen Content (%) × Conversion Factor

Jones Factors by Food Type

Jones conversion factors vary significantly by food type

Using 6.25 for all foods typically overestimates protein content