| Sample | Mode | Nitrogen (%) | Factor | Protein (% as-is) | Moisture (%) | Protein (% dry basis) |
|---|---|---|---|---|---|---|
| Milk powder | Direct | 5.20 | 6.38 | 33.18 | 4.0 | 34.56 |
| Wheat flour | Direct | 2.10 | 5.70 | 11.97 | 12.5 | 13.69 |
| Feed sample | Kjeldahl | 3.05 | 6.25 | 19.06 | 10.0 | 21.18 |
- Choose Direct nitrogen (%) if you already have nitrogen results.
- Choose Kjeldahl titration if you have volumes and normality.
- Set a suitable conversion factor for your material.
- Add moisture to get dry-basis protein, if needed.
- Press Calculate; results appear above the form.
- Use CSV or PDF buttons to download reports.
Nitrogen-to-protein conversion in analytical chemistry
Many food and feed labs estimate protein by measuring total nitrogen and applying a conversion factor. The default 6.25 assumes proteins contain 16% nitrogen, but real materials vary. For example, dairy proteins often use 6.38, while many cereal products use about 5.70.
Direct nitrogen entry for rapid reporting
When nitrogen percentage is already available from an instrument report, this calculator converts it to protein instantly. A 2.10% nitrogen result with factor 5.70 yields 11.97% protein as-is. This workflow is useful for quick label checks, intake verification, and routine screening.
Kjeldahl titration pathway for detailed lab data
In the titration pathway, blank-corrected volume is translated to grams of nitrogen using the nitrogen atomic mass (14.007). Normality controls moles per liter, so accurate standardization matters. The multiplier lets you scale from an aliquot to the full digest, combining dilution steps into one value.
Moisture adjustment and dry-basis comparability
“As-is” protein is reported on the current moisture level, while “dry basis” removes water to compare batches fairly. Dry basis equals as-is divided by (1 − moisture/100). For 19.06% as-is protein at 10.0% moisture, dry-basis protein becomes about 21.18%.
Quality controls that reduce calculation risk
Reliable protein estimates depend on representative sampling, consistent digestion, and stable titration endpoints. Record blanks, run duplicates, and track drift in normality. If blank exceeds sample volume, the calculator floors the difference at zero to avoid negative nitrogen artifacts.
Interpreting outputs for specification decisions
Use nitrogen (%) to validate lab chemistry steps and protein (%) to evaluate product compliance. Dry-basis values help compare raw materials with different moisture targets. Exported CSV supports audits, while the PDF summary helps share results with production, procurement, or QA teams.
Which conversion factor should I use?
Use the factor specified by your standard method or product spec. Common values include 6.25 (general), 6.38 (dairy), and about 5.70 (many cereals). Keep it consistent within a program.
Why does dry-basis protein look higher?
Dry-basis removes the water fraction. If moisture is present, the same protein mass is distributed over less dry matter, so the percentage increases. This supports fair comparisons across different moisture levels.
What does the overall multiplier represent?
It scales nitrogen from the measured aliquot to the whole digest, and can include dilution factors. For example, if you titrate 10 mL from a 100 mL digest, the multiplier may be 10.
Can protein exceed 100% in the results?
It can happen from unrealistic inputs, extreme multipliers, or unit mistakes. The calculator allows high values for troubleshooting, but you should verify volumes, normality, and sample weight to correct the setup.
Why do I need a blank value in titration mode?
The blank captures nitrogen contribution from reagents and handling. Subtracting it reduces bias and improves accuracy. If blank volume is larger than sample volume, the calculator uses zero difference to prevent negative nitrogen.
What is included in the exported CSV and PDF?
Exports include the calculation mode and the main outputs: nitrogen, protein as-is, protein dry basis, protein mass estimate, conversion factor, and moisture. Generate a new export after each run for clean records.