Crude Fibre Calculator
Calculate crude fibre as a percentage of dry sample weight. Enter the crucible and residue weights before and after ashing, plus the original dry sample weight.
Calculate Crude Fibre Percentage
Crude Fibre Formula
Where:
- \(W_{\text{before}}\) — weight of the crucible and dried residue before ashing (g)
- \(W_{\text{after}}\) — weight of the same crucible and residue after ashing (g)
- \(W_{\text{sample}}\) — original dry sample weight (g)
Ashing burns away the organic material left in the prepared residue. Subtracting the two crucible weights gives the mass lost during ashing; dividing by the original dry sample weight expresses that loss as a percentage.
Crude Fibre – Calculation Example
Example: a 0.52 g dry feed sample produces a crucible-and-residue weight of 2.46 g before ashing and 1.94 g after ashing.
\[\text{Crude fibre (\%)}=\frac{2.46-1.94}{0.52}\times100=100\%\]
Result: 100% crude fibre. These default values demonstrate the calculation, but the result is unusually high for a real sample; check the measurements and sample preparation before interpreting it.
How to use the calculator
- Enter the Weight before ashing in grams: the combined weight of the crucible and the dried, prepared residue.
- Enter the Weight after ashing in grams: the combined weight of the same crucible and the ash remaining in it.
- Enter the Sample weight in grams: the original dry weight of the portion used for analysis, before digestion.
- Read Percentage of Crude Fibre. The calculator subtracts the after-ashing weight from the before-ashing weight, divides by the sample weight, and rounds the percentage to two decimal places.
All three entries must use the same mass unit. The fields are marked in grams, and using grams throughout makes the measurements easy to check. The sample weight must be greater than zero or the calculator displays an error.
What crude fibre measures
Crude fibre is an operational laboratory measurement of material left after a food or feed sample undergoes specified dilute acid and alkali treatments. The treated residue is dried and weighed, then ashed and weighed again. The loss in mass on ashing is attributed to organic material in that residue and reported relative to the original sample.
The result is useful for describing and comparing feeds tested by the same method. For example, it can help characterize the fibrous portion of plant-based feed alongside other composition measurements, such as crude protein. A value of 12% means the measured mass lost during ashing was 0.12 g for each 1 g of original dry sample—not that precisely 12% of every type of plant fibre was recovered.
Crude fibre is not the same as total dietary fibre. Some fibre components can dissolve or break down during the acid and alkali treatments, so the crude fibre method may report less than other fibre methods. It also does not directly measure how much of a feed an animal can digest. Compare results only when the analytical method and the basis of reporting are clear.
Assumptions and measurement checks
This calculation assumes that the two crucible weights refer to the same crucible and the same prepared residue. Its subtraction cancels the crucible’s mass; no separate crucible-weight entry is needed. The before-ashing residue should be dried as required by the laboratory procedure, and the after-ashing measurement should be taken after ashing and cooling as required by that procedure. Moisture left in the residue, spilled material, or an unclean crucible can distort the difference.
The calculator uses the original dry sample weight as its denominator. If the weighed sample was moist, determine its dry weight before using this field. Otherwise, the result will be on a different basis and may not be comparable with dry-basis results. Keep more precision in the measured masses than in the displayed percentage: a small weighing error can have a large effect when the sample is small.
Check that Weight before ashing exceeds Weight after ashing and that the calculated mass loss does not exceed the original dry sample weight. The calculator only rejects a sample weight of zero or less; it does not validate the other measurements. A negative result or one above 100% calls for a review of the entries and laboratory procedure. The default entries give exactly 100%, which is mathematically valid but warrants that review rather than being treated as a typical feed result.
The ash left after heating is not, by itself, a measurement of any one mineral. If calcium content is the quantity you need, use a calcium-specific analysis and the Estimation of Calcium Calculator instead.
Frequently Asked Questions
How can I check a crude fibre calculation by hand?
Find the mass lost during ashing, then express it as a percentage of the original dry sample. For example, if the two crucible weighings differ by 0.105 g and the dry sample weighed 1.50 g, the result is \(0.105/1.50\times100=7\%\). Use the same crucible for both weighings so its mass cancels out.
What is a normal crude fibre percentage for animal feed?
There is no single normal or good percentage for all feeds. Crude fibre varies with the ingredient, plant maturity, processing, and the animal the feed is intended for. Compare a result with specifications for the particular feed type, using values measured by the same laboratory method and reported on the same moisture basis. Crude fibre alone does not establish feed quality.
How do I convert crude fibre percent to g/kg or mg/kg?
Multiply the percentage by 10 to get grams per kilogram, or by 10,000 to get milligrams per kilogram. For example, 8% crude fibre equals 80 g/kg or 80,000 mg/kg. These are different units for the same mass fraction; they do not change whether the result is reported on a dry-matter or as-fed basis.
How do I convert dry-basis crude fibre to an as-fed value?
Multiply the dry-basis crude fibre percentage by the feed’s dry-matter fraction. If a feed contains 20% moisture, its dry-matter fraction is 0.80, so 12% crude fibre on a dry basis equals \(12\%\times0.80=9.6\%\) as fed. Use moisture measured for the same feed sample or batch; otherwise, the conversion is only an estimate.
What does a crude fibre result of 0% mean?
A 0% result means the recorded crucible weights before and after ashing were equal, or their difference rounded to zero in the displayed result. It does not prove that the sample contains no fibre. Check the unrounded weights, balance precision, sample size, and whether the prepared residue was handled correctly. A very small mass loss may be below the method’s reliable measurement range.
Is crude fibre the same as NDF or ADF?
No. Neutral detergent fibre (NDF) and acid detergent fibre (ADF) use different laboratory treatments and describe different residue fractions. They are often used in forage evaluation, but an NDF or ADF value cannot be reliably calculated from a crude fibre percentage. Use the measurement specified by the feed standard, ration model, or comparison you are working with.
Should I subtract a laboratory blank from the crude fibre result?
Follow the laboratory method’s instructions for blanks and corrections. A blank can reveal mass changes caused by reagents, filter aids, or the procedure rather than the sample. If the method requires a blank correction, apply it to the measured residue mass loss before dividing by the sample weight; this calculator does not apply that correction automatically. Do not subtract a blank unless its preparation and units match the method.