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Crude Protein Calculator

Chemistry

Calculate crude protein content from total nitrogen using the Kjeldahl method. Crude Protein (%) = % Nitrogen × 6.25 (or food-specific conversion factors).

090
100

Crude Protein (%)

15.63
Protein Mass (g)
15.625
Nitrogen Mass (g)
2.5

This calculator computes your Crude Protein (%), Protein Mass (g), Nitrogen Mass (g) from the values you enter.

Inputs
Total Nitrogen (%)Conversion Factor (F)Sample Mass (g)
Outputs
Crude Protein (%)Protein Mass (g)Nitrogen Mass (g)

What is a Crude Protein?

The Crude Protein Calculator converts total nitrogen percentage to crude protein content using food-specific Kjeldahl conversion factors: Crude Protein (%) = %N × F. Select the appropriate conversion factor for your food type and enter the nitrogen percentage from analytical measurement.

Crude protein is the standard method for estimating protein content in food, feed, and agricultural products. It was developed alongside the Kjeldahl nitrogen determination method (1883) and remains the primary assay for protein labelling under FSSAI (India), FDA (USA), EFSA (EU), and Codex Alimentarius international standards. The term "crude" acknowledges that the method measures all nitrogen, not just protein nitrogen — non-protein nitrogen sources (NPN: urea, nucleic acids, creatinine) contribute to the reading.

For converting dry-weight nitrogen measurements to protein mass in a given sample, the Percent Composition Calculator and Molar Mass Calculator provide the elemental chemistry background. For enzyme-based protein characterisation, the Enzyme Activity Calculator and Michaelis-Menten Calculator handle kinetic parameters.

How to use this Crude Protein calculator

  1. Run a Kjeldahl or Dumas nitrogen analysis on your food sample to get Total Nitrogen (%).
  2. Select the Conversion Factor matching your food type from the dropdown.
  3. Enter Sample Mass if you need the absolute protein mass.
  4. Read Crude Protein (%) — this is the value for FSSAI nutrition labels.
  5. Cross-check: typical values — dal ~25%, chicken ~30%, milk ~3.4%, wheat flour ~12%.

Formula & Methodology

Crude protein by Kjeldahl factor:

Crude Protein (%) = %N × F Protein Mass (g)  = (CP% / 100) × sample_mass_g

Standard conversion factors:

F = 6.25: General / mixed diet / meat / fish F = 5.70: Wheat / cereal grains (gluten is higher-N protein) F = 6.38: Milk / dairy products (casein composition) F = 5.46: Soybean (high N content in soy protein) F = 5.30: Rice F = 5.83: Legumes / pulses

Worked example — masoor dal (red lentil) analysis:

Kjeldahl analysis of masoor dal gives %N = 3.7%.

Using F = 5.83 (legumes):

CP = 3.7 × 5.83 = 21.57% ≈ 21.6% crude protein For 100 g dal: protein = 21.6 g

This matches ICMR-NIN published values for masoor dal (~22% CP on dry weight). For the packaged dal consumed in Indian kitchens, FSSAI requires this value on the nutrition label. India produces ~25 million tonnes of pulses annually — the world's largest producer and consumer — making crude protein analysis a high-volume analytical operation across hundreds of food testing laboratories under NABL accreditation.

Frequently Asked Questions

Crude protein (CP) is the estimated total protein content of a food or feed sample, calculated from its total nitrogen content: CP (%) = %N × F, where F is a food-specific conversion factor (6.25 for most foods, 5.70 for wheat, 6.38 for dairy). The name 'crude' reflects that it overestimates true protein because it includes non-protein nitrogen (NPN) — urea, nucleic acids, free amino acids — that also contain nitrogen but are not dietary protein. True protein requires separating NPN from actual protein nitrogen, which is more analytically demanding.
The factor 6.25 assumes that protein contains approximately 16% nitrogen by mass: 1/0.16 = 6.25. This approximation is based on the average amino acid composition of mixed dietary proteins (most proteins contain 15–18% N). The factor 6.25 = 100/16 converts %N to %crude protein. It was first proposed by Kjeldahl in 1883 alongside his nitrogen determination method. Different protein sources have different amino acid compositions and thus different N content: dairy proteins (~15.7% N → F=6.38), wheat gluten (~17.5% N → F=5.70), soy (~18.3% N → F=5.46).
Enter the Total Nitrogen (%) from a Kjeldahl or Dumas nitrogen analysis and select the appropriate Conversion Factor for your food type (6.25 for general/mixed diet, 5.70 for cereals, 6.38 for dairy, 5.46 for soy, 5.30 for rice, 5.83 for legumes). Enter Sample Mass (g) if you want the protein mass in grams. The calculator returns Crude Protein (%), Protein Mass (g), and Nitrogen Mass (g).
The Kjeldahl method (1883) is the standard analytical technique for total nitrogen: (1) Digestion: sample is heated with concentrated H₂SO₄ + catalyst (Cu or Se) → all N converted to (NH₄)₂SO₄. (2) Distillation: NaOH is added → NH₃ gas is distilled. (3) Titration: NH₃ is absorbed in boric acid → back-titrated with HCl to find total N. The modern Dumas method (ISO 16634) is faster: sample is combusted, N₂ measured by thermal conductivity — same accuracy, no hazardous H₂SO₄. FSSAI mandates the Kjeldahl or Dumas method for crude protein determination in Indian food labelling.
Dal (masoor dal): ~25% CP (cooked: ~9%). Soya chunks: ~52% CP. Paneer (cottage cheese): ~18% CP. Chicken breast: ~31% CP. Moong dal: ~24% CP. Toor dal: ~22% CP. Wheat flour: ~12% CP. Brown rice: ~8% CP. Milk (cow): ~3.4% CP. Rajma (kidney beans): ~24% CP. Groundnuts: ~26% CP. These values from ICMR-NIN (Indian Council of Medical Research-National Institute of Nutrition) food composition tables use food-specific conversion factors; labels may vary if using the generic F=6.25.
The Food Safety and Standards (Labelling and Display) Regulations, 2020 (FSSAI) require: (1) Nutrition information label mandatory for packaged foods with >19 kcal per 100g. (2) Protein declaration required in g per 100g (and optionally per serving). (3) %RDA declaration based on 2000 kcal reference diet with 50g protein. High protein claim: ≥12g protein per 100g solid food or ≥6g per 100 kcal. FSSAI uses the Kjeldahl-derived crude protein value using standard conversion factors (F=6.25 for most foods, food-specific factors for dairy and cereals).
Crude protein measures all nitrogen × F — includes non-digestible proteins, non-protein nitrogen, and anti-nutritional factors. Digestible protein (or apparent protein digestibility) accounts for the fraction actually absorbed: Digestible protein = CP × PD, where PD = protein digestibility coefficient (0 = indigestible, 1 = fully digestible). For eggs: PD ≈ 0.97 (nearly complete absorption). For meat: PD ≈ 0.94. For wheat: PD ≈ 0.86. For legumes: PD ≈ 0.78–0.85. Protein Digestibility-Corrected Amino Acid Score (PDCAAS) — the global standard — combines amino acid profile with digestibility for protein quality assessment.
By crude protein content: animal sources (meat 20–35%, eggs 13%, dairy 3–18%) generally have lower CP% by fresh weight but higher protein quality (complete amino acid profiles). Plant sources often have higher CP% on dry weight basis (soy 36–52%, pulses 20–25%) but lower in one or more essential amino acids (cereals lack lysine; legumes lack methionine). Indian diets combining rice + dal or roti + dal achieve complementary amino acid profiles. ICMR recommends 0.8–1.0 g protein/kg body weight/day for adults; Indian National Nutrition Monitoring Bureau surveys show average Indian adult protein intake is ~50–60g/day.
Yes — this is a significant food safety concern. Melamine (C₃H₆N₆, 66.6% N) was famously used to fraudulently inflate crude protein readings in Chinese milk powder (2008 scandal, affecting 300,000 infants). Since the Kjeldahl method measures total nitrogen without distinguishing protein from non-protein sources, adding melamine to food artificially raises apparent CP. Regulatory response: FSSAI now mandates melamine testing (by HPLC) for imported dairy products and infant formula. True protein tests (Bradford assay, Lowry assay, direct amino acid analysis) can detect such adulteration.
ICMR-NIN 2020 Recommended Dietary Allowances for Indians: Sedentary adult men: 54 g/day. Sedentary adult women: 46 g/day. Pregnant women: 54 g/day + 23 g extra = 77 g/day. Lactating women: 54 + 19 g/day = 73 g/day. Children 1–3 years: 12.5 g/day. Adolescents (10–12 years, boys): 54 g/day. Athletes: 1.2–1.7 g/kg body weight/day. India's National School Mid-Day Meal Programme targets 12g protein per meal for primary school children using dal, egg, or groundnut as the protein source, formulated using crude protein calculations.