What this calculator does
Feed labels give nutrient percentages as fed, which makes two feeds of different moisture content impossible to compare directly. A wet feed looks low in protein simply because a large part of what is being weighed is water.
Dry matter basis strips the water out. The conversion is the as-fed percentage multiplied by 100 and divided by 100 minus the moisture percentage. A 25% protein feed at 10% moisture is 27.8% on a dry matter basis, and the same 25% at 50% moisture is 50%, which is a completely different feed.
The formula
The dry matter fraction is 100 minus the moisture percentage. The as-fed nutrient percentage is divided by that fraction and multiplied by 100, which rescales the figure as though all the water had been removed. Any nutrient can be converted this way, and every nutrient in a feed should be converted before comparing against another feed.
| Term | Meaning |
|---|---|
| As-fed basis | The percentage as the feed is actually delivered, water included. |
| Dry matter basis | The percentage with all water removed, which is the only fair basis for comparison. |
| Moisture content | The percentage of the feed that is water. Dry feeds run around 10%, wet feeds 70% or more. |
The inputs explained
| Field | What to enter |
|---|---|
| As-fed nutrient percentage (%) | The nutrient percentage as printed on the label, on an as-fed basis. |
| Moisture content (%) | Moisture content as a percentage. If the label gives dry matter instead, subtract it from 100. |
When to use it
Comparing wet and dry pet food
Tinned food at 78% moisture and dry food at 10% cannot be compared as labelled. Converting both to dry matter is the only way to see which actually has more protein per unit of nutrition.
Ration formulation for livestock
Silage, hay and grain differ enormously in moisture, so rations are formulated on a dry matter basis throughout and converted back to as-fed only at the point of weighing out.
Checking a supplier specification
Specifications are sometimes quoted on one basis and sometimes the other, and converting is how you find out whether two quotes describe the same thing.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How does moisture content change the dry matter figure?
The same 25% as-fed percentage across a range of moisture contents.
| Moisture content | Dry-matter-basis percentage | As-fed percentage used | Moisture content used |
|---|---|---|---|
| 5% | 26.32 % | 25.00 % | 5.00 % |
| 10% | 27.78 % | 25.00 % | 10.00 % |
| 20% | 31.25 % | 25.00 % | 20.00 % |
| 50% | 50.00 % | 25.00 % | 50.00 % |
Questions
Why convert to dry matter at all?
Because water contributes weight but no nutrition. A feed that is three-quarters water has its nutrient percentages diluted by that water, so comparing it against a dry feed on the label figures makes it look far worse than it is. Dry matter removes the dilution from both sides.
How do I compare wet and dry pet food?
Convert both to dry matter basis first. Tinned food at around 78% moisture and dry food at around 10% will often turn out to be much closer in protein than the labels suggest, and sometimes the wet food is higher.
Where do I find the moisture content?
On the guaranteed analysis or feed label, usually as a maximum moisture figure. If only dry matter is given, moisture is 100 minus that. Where neither appears, typical values are around 10% for dry feeds, 65 to 70% for silage and 75 to 80% for tinned pet food.
Does this work for any nutrient?
Yes, the conversion is the same for protein, fat, fibre or anything else expressed as a percentage of the feed. Convert every nutrient you intend to compare, since converting one and not another produces a mixed comparison that is worse than no conversion at all.
For feed efficiency once the ration is set, see the feed conversion ratio calculator. For fertiliser dosing on the cropping side, see the fertilizer application rate calculator.