Calculating protein on a dry matter basis takes four seconds once you know the steps, and it is the single most useful bit of label arithmetic in pet food. This guide is a how-to: the formula, a step-by-step method, a table of conversions for common moisture levels, worked examples for dogs and cats and a few checks so you know you have done it right. For the idea behind it, see our introduction to dry matter basis.
The formula
dry matter protein % = label protein % ÷ (100 − moisture %) × 100
The denominator, 100 minus the moisture percentage, is the share of the food that is not water. Dividing by it scales the protein up to what it would be if the water were removed. The Dry Matter Basis Calculator does the same for protein, fat and fibre at once.
Step by step
- Find the guaranteed analysis or analytical constituents on the label.
- Write down moisture (maximum) and crude protein (minimum).
- Subtract moisture from 100. For 78% moisture the result is 22.
- Divide protein by that number: 8 ÷ 22 = 0.364.
- Multiply by 100: 36.4%.
If you want the as-fed value again, reverse it: 36.4 × 22 ÷ 100 = 8.
A quick lookup table
For a label protein of 8% (a typical wet food), the dry matter result depends on moisture:
| Moisture | Dry matter (100 − moisture) | Protein 8% as fed | Protein on a dry matter basis |
|---|---|---|---|
| 70% | 30% | 8% | 26.7% |
| 75% | 25% | 8% | 32.0% |
| 78% | 22% | 8% | 36.4% |
| 80% | 20% | 8% | 40.0% |
| 82% | 18% | 8% | 44.4% |
And for a dry food at 26% protein as fed:
| Moisture | Dry matter | Protein 26% as fed | Protein on a dry matter basis |
|---|---|---|---|
| 6% | 94% | 26% | 27.7% |
| 8% | 92% | 26% | 28.3% |
| 10% | 90% | 26% | 28.9% |
| 12% | 88% | 26% | 29.5% |
Notice that moisture matters much more for wet foods: a few percentage points of moisture change the result by several points. For a kibble, the effect is small.
Worked examples
A wet dog food. Moisture 78%, protein 8%, fat 5%, fibre 1.5%.
- Dry matter: 22%.
- Protein: 8 ÷ 22 = 36.4%.
- Fat: 5 ÷ 22 = 22.7%.
- Fibre: 1.5 ÷ 22 = 6.8%.
A dry dog food. Moisture 10%, protein 26%, fat 16%.
- Dry matter: 90%.
- Protein: 26 ÷ 90 = 28.9%.
- Fat: 16 ÷ 90 = 17.8%.
A cat pouch. Moisture 82%, protein 9%, fat 6%.
- Dry matter: 18%.
- Protein: 9 ÷ 18 = 50.0%.
- Fat: 6 ÷ 18 = 33.3%.
A semi-moist food. Moisture 30%, protein 18%, fat 10%.
- Dry matter: 70%.
- Protein: 18 ÷ 70 = 25.7%.
- Fat: 10 ÷ 70 = 14.3%.
Comparing the four, the pouch has the highest protein on a dry matter basis, and the semi-moist food has the lowest, even though the semi-moist food has more protein on the label than the pouch. This is why comparing label numbers across types of food misleads.
Checking your arithmetic
A few checks catch most mistakes:
- The dry matter result must always be larger than the as-fed result if moisture is above zero.
- If moisture is zero, the two are the same.
- The result for a wet food is usually in the 25 to 55% range for protein, so a result of 2% or 400% means a slip.
- Converting back should give the original: 36.4% × 22% = 8.0%.
- If you use the calculator and your own sum disagrees, check the moisture figure first.
Rounding
Round to one decimal place at most. The label’s figures are themselves rounded or stated as minimums, so extra decimals do not mean extra accuracy. A difference of one or two points between two foods on a dry matter basis is within the noise of the label.
What to do with the result
Once you have dry matter protein, you can compare any two foods on equal terms. But remember what the number is and is not:
- It describes concentration, not quality or suitability.
- A food must be complete and balanced for the pet’s life stage.
- Pets with certain health conditions need diets set by a vet.
- Protein is only one nutrient; fat, fibre and minerals also matter.
- The number does not say how many calories the food supplies. For that, use the Dog Food Calorie Calculator or the label’s kcal figure.
If you want to compare cost, the fairest way is price per 1,000 kcal using the Pet Food Price per 1,000 kcal Calculator.
Doing it for fat and fibre
The same formula works for any nutrient on the label. For example, a food with 82% moisture and 6% fat has 6 ÷ 18 × 100 = 33.3% fat on a dry matter basis. You can also work out carbohydrate by difference: 100 minus protein, fat, fibre, moisture and ash (all as fed), then divide by dry matter. The modified Atwater method for energy uses these values; our calculator for food calories shows the steps.
A short example you can try
A cat owner is comparing two foods:
| Food A (pouch) | Food B (kibble) | |
|---|---|---|
| Moisture | 80% | 9% |
| Protein as fed | 10% | 33% |
- Food A: 10 ÷ 20 × 100 = 50.0%.
- Food B: 33 ÷ 91 × 100 = 36.3%.
On the label B looks more than three times richer, but on a dry matter basis A is higher. Neither is “better”, they are just different in concentration, and the owner should choose on the pet’s needs, the vet’s advice and the other nutrients and calories.
Common mistakes
- Dividing by the moisture figure instead of 100 minus moisture.
- Forgetting to multiply by 100.
- Mixing up as-fed and dry matter percentages in the same comparison.
- Treating a higher result as a higher quality.
- Using typical values from a website instead of the label.
- Rounding too early.
Practice problems with answers
Working a few examples by hand makes the method automatic. Try each before reading the answer.
| Problem | Moisture | Label protein | Answer (DM protein) |
|---|---|---|---|
| 1. A wet dog food | 75% | 9% | 9 ÷ 25 × 100 = 36.0% |
| 2. A wet cat food | 80% | 11% | 11 ÷ 20 × 100 = 55.0% |
| 3. A dry cat food | 8% | 36% | 36 ÷ 92 × 100 = 39.1% |
| 4. A dry dog food | 12% | 22% | 22 ÷ 88 × 100 = 25.0% |
| 5. A semi-moist treat | 25% | 15% | 15 ÷ 75 × 100 = 20.0% |
| 6. A rehydrated dehydrated food | 70% | 7.5% | 7.5 ÷ 30 × 100 = 25.0% |
Notice problem 6: a dehydrated food looks very high in protein when dry, but once it is rehydrated for serving it is much more dilute. The same product can be compared two ways, as sold (dry) or as fed (rehydrated), so be clear about which label figure you use and keep the moisture figure to match.
Converting back: from dry matter to as fed
If a vet or a nutrition guideline gives a requirement on a dry matter basis, you may want to know what that means on a label. Reverse the formula:
as-fed % = dry matter % × (100 − moisture %) ÷ 100
A target of 30% protein on a dry matter basis, for a wet food at 78% moisture, is 30 × 22 ÷ 100 = 6.6% on the label. For a dry food at 10% moisture it is 30 × 90 ÷ 100 = 27% on the label. This is why you can find a wet food with 7% on the can that meets a requirement that a dry food needs 27% to meet.
Per 1,000 kcal: the other fair comparison
Dry matter basis removes water, but foods also differ in calories per gram, so some nutrition guidelines express nutrients per 1,000 kcal. The sum is: protein per 1,000 kcal = protein grams per kg of food ÷ kcal per kg × 1,000. For a wet food with 80 g of protein per kg (8%) and 1,000 kcal per kg, that is 80 g per 1,000 kcal. For a dry food with 340 g of protein per kg (34%) and 3,800 kcal per kg, it is about 89 g per 1,000 kcal. The extra step matters when you compare foods with very different fat levels, since fat adds calories without adding protein.
What the numbers do not show
- Digestibility. Two foods with the same protein percentage can supply different amounts of usable protein.
- Amino acid balance. The mix of amino acids matters as well as the total.
- The rest of the nutrient profile. Fat, minerals and vitamins matter.
- Your pet’s needs. A pet with kidney or liver problems may need a different protein level, and only a vet can advise.
Treat the dry matter percentage as a first filter, and talk to your vet before changing a diet because of it.
A checklist for any label
When you pick up a bag or can, run the same five checks so you never compare as-fed numbers across different formats.
- Find the moisture figure in the guaranteed analysis.
- Subtract it from 100 to get the dry matter percentage.
- Divide each nutrient by the dry matter percentage and multiply by 100.
- Write the result next to the as-fed figure so you can see both.
- Compare only dry matter figures between foods.
For a dry food with 10% moisture and 26% protein, dry matter is 90% and protein is 26 ÷ 90 × 100 = 28.9%. For a wet food with 78% moisture and 9% protein, dry matter is 22% and protein is 9 ÷ 22 × 100 = 40.9%. The wet food has the higher dry matter protein, though its label figure is lower. Our guide to why wet food looks low in protein walks through the reason.
Common slips
- Using the as-fed number in the numerator but the wrong moisture in the denominator.
- Forgetting that ash and fibre also shift when you convert.
- Comparing a dry matter figure from one brand with an as-fed figure from another.
- Treating a high percentage as a sign of better quality; the percentage says nothing about digestibility or ingredients.
Quick summary
- Dry matter protein % = label protein % ÷ (100 − moisture %) × 100.
- A wet food at 78% moisture and 8% protein is 36.4%; a kibble at 10% moisture and 26% protein is 28.9%.
- The same steps work for fat, fibre and any other label nutrient.
- Check that the answer is larger than the label figure and that converting back gives the original.
- The number measures concentration, not quality.
- Use the Dry Matter Basis Calculator to skip the arithmetic.
Frequently asked questions
How do I calculate protein on a dry matter basis?
Divide the label protein percentage by (100 minus moisture percentage), then multiply by 100.
What is 8% protein at 78% moisture on a dry matter basis?
8 ÷ 22 × 100 = 36.4%.
What is 26% protein at 10% moisture on a dry matter basis?
26 ÷ 90 × 100 = 28.9%.
Do I use the same method for fat and fibre?
Yes. Replace protein with the nutrient you want and use the same moisture figure.
Does ash matter?
Ash is part of dry matter, and it can be used to estimate carbohydrate by difference, but it does not change the protein calculation.
What if the label gives a range for moisture?
Use the stated maximum for a conservative result, or the typical value if the label shows one, and remember the answer is approximate.
Can I convert back from dry matter to as fed?
Yes. As fed % = dry matter % × (100 − moisture %) ÷ 100.
Sources
- WSAVA Global Nutrition Guidelines
- NRC (2006) Nutrient Requirements of Dogs and Cats, National Academies Press
- Pure arithmetic: dry matter nutrient % = label nutrient % ÷ (100 − moisture %) × 100
Related calculators
- Dry Matter Basis CalculatorCompare wet and dry pet foods fairly by removing the water from the label percentages.
- Dog Food Calorie CalculatorWork out how many calories are in a dog or cat food from the nutrient percentages (guaranteed analysis) on its label, when no kcal figure is printed.
- Pet Food Price per 1,000 kcal CalculatorCompare two foods fairly by price per 1,000 calories instead of price per bag.
Keep reading
- Dry Matter Basis: Compare Wet and Dry FoodLearn how dry matter basis works, the formula to convert any pet food label, worked examples for wet, dry and semi-moist foods and common label traps.
- Why Wet Food Looks Low in Protein on the LabelWhy wet pet food shows low protein on the label: water dilutes every percentage. See the conversion, side-by-side examples and how to compare fairly.
- How Much Should I Feed My Dog? By WeightHow much to feed a dog by weight: a grams and cups chart, how to read the food label, meals per day, adjusting by body condition and common mistakes.