Pet food labels are written for shoppers, not for scientists, and one of the biggest traps is water. A can of wet food and a bag of kibble can contain the same amount of protein per mouthful of dry ingredients, yet the labels will show very different numbers because one product is mostly water. Dry matter basis is the simple fix: take the water out of the sum, and compare what is left. This guide explains the idea, the formula, worked examples and the mistakes people make when they read labels.
What “as fed” means on a label
The percentages in a guaranteed analysis describe the food as fed, which means exactly as it comes out of the can or bag, water included. A typical wet food lists moisture of around three quarters of its weight, while a dry kibble lists a small fraction. Every other number on the panel, whether protein, fat, fibre or ash, is a share of that total weight. So when a can says “8% protein” and a bag says “26% protein”, you are comparing two different things: a nutrient share of a watery food and a nutrient share of a nearly dry one.
This is not a flaw in the label, it is just a convention. The label reports what is in the container. To compare two foods fairly you need to remove the one ingredient that differs most between them, which is water.
The dry matter formula
Dry matter is everything in the food except water, so it is 100 minus the moisture percentage. To express any nutrient on that basis:
dry matter nutrient % = label nutrient % ÷ (100 − moisture %) × 100
The Dry Matter Basis Calculator does this for protein, fat and fibre at once. If a food is 78% moisture, its dry matter is 22%. A nutrient at 8% as fed is 8 ÷ 22 = 0.364 of the dry matter, which is 36.4%.
Worked examples: wet, dry and semi-moist
| Food type | Moisture | Protein as fed | Fat as fed | Dry matter | Protein (DM) | Fat (DM) |
|---|---|---|---|---|---|---|
| Wet (can) | 78% | 8% | 5% | 22% | 36.4% | 22.7% |
| Dry (kibble) | 10% | 26% | 16% | 90% | 28.9% | 17.8% |
| Very wet (pouch) | 82% | 9% | 6% | 18% | 50.0% | 33.3% |
| Semi-moist | 30% | 18% | 10% | 70% | 25.7% | 14.3% |
Look at the first two rows. On the label the kibble has more than three times the protein of the can (26% against 8%), yet on a dry matter basis the can is higher (36.4% against 28.9%). Neither number says one food is better. They say that the can is concentrated once the water is ignored, and that you would have to feed a lot more of it, by weight, to deliver the same dry matter.
Why this matters when you compare foods
Imagine you are choosing between a wet food and a dry food for a cat. If you compare as-fed protein you will conclude that the dry food has three times as much, and the wet food looks weak. If you compare on a dry matter basis you will see that the two are in the same range. Dry matter basis therefore protects you from two opposite mistakes: dismissing wet foods as low in nutrients, and assuming a food is rich in protein just because its label figure is large.
It also helps when you switch between formats. A pet moving from kibble to wet food will find that the grams change a lot but the nutrient density on a dry matter basis may stay similar, which is a useful check on whether a change is a large change or a small one.
It is not a quality score
Dry matter basis tells you how concentrated a nutrient is. It does not tell you whether the food is good for your pet. A food needs to be complete and balanced for the right life stage, which means it provides all the nutrients that pet needs in the right proportions. A higher number is not automatically better: too much of some nutrients can be a problem for pets with certain health conditions, and your vet may recommend a specific diet for a particular pet. Use dry matter basis as a way to read the label accurately, then discuss the choice with your vet.
Dry matter basis and calories are different things
People often assume that more protein or fat on a dry matter basis means more calories, and while there is a link, the two are not interchangeable. Calories depend on protein, fat and carbohydrate together, and the label may not list carbohydrate at all. To estimate energy when a kcal figure is not printed, use the NRC’s modified Atwater factors with the Dog Food Calorie Calculator, which turns protein, fat, fibre, moisture and ash into kcal per kg. Our guide to how many calories a dog needs explains how that energy figure becomes a feeding amount.
How to find the moisture figure
The moisture percentage is in the guaranteed analysis, usually as “moisture (max)”. A few practical notes:
- Wet foods in cans, pouches and trays usually show the highest moisture; check each product because they are not all the same.
- Dry foods usually list a low moisture value, often around a tenth of the weight.
- If the label lists only a nutrient panel with no moisture, the maker can supply it. Without it you cannot do the conversion accurately.
- Some labels show “typical” values rather than guaranteed minimums and maximums. Use whichever is given, and remember that it is an approximation.
Step by step: converting any label
- Write down the moisture percentage.
- Subtract it from 100 to get the dry matter percentage.
- For each nutrient you want, divide the as-fed percentage by the dry matter percentage and multiply by 100.
- Do the same for the other food and compare the results.
For example, a pouch lists 82% moisture and 9% protein. Dry matter is 18%, so protein is 9 ÷ 18 × 100 = 50%. A kibble lists 10% moisture and 26% protein: 26 ÷ 90 × 100 = 28.9%. The pouch is more concentrated in protein once the water is ignored.
Comparing cost: dry matter and calories together
The fairest cost comparison does not use bag price or even dry matter protein, it uses price per 1,000 kcal, because calories are what the pet actually needs. The Pet Food Price per 1,000 kcal Calculator compares two foods in one step. Use dry matter basis to read nutrients accurately, and use price per 1,000 kcal to compare cost. If your labels list energy in different units, the Pet Food Energy Converter makes them match.
Typical label traps
- Comparing as-fed protein across formats. The most common mistake, and the reason for this guide.
- Forgetting that moisture differs between batches. Moisture is a maximum, and actual values vary a little.
- Using dry matter basis to judge quality. It measures concentration, not suitability.
- Mixing up percent and grams. A nutrient percentage is a share of weight, not an amount per serving.
- Ignoring ash and fibre. They are part of dry matter and matter for energy estimates.
A note on ingredient lists
Ingredients are listed by weight before cooking, so an ingredient with a lot of water, such as fresh meat, can appear near the top of the list even though it contributes less dry matter than a dried ingredient further down. The same water effect that distorts nutrient percentages also distorts ingredient order. This is another reason that the ingredient list alone is a poor guide to the nutrient content of a food; the guaranteed analysis converted to a dry matter basis is more reliable.
Dry matter basis for cat food
The arithmetic is the same for cats, but the typical foods differ, and a quick table helps.
| Cat food | Moisture | Protein as fed | Fat as fed | Protein (DM) | Fat (DM) |
|---|---|---|---|---|---|
| Wet pâté | 78% | 10% | 6% | 45.5% | 27.3% |
| Wet in gravy | 82% | 8% | 3% | 44.4% | 16.7% |
| Dry kibble | 9% | 34% | 15% | 37.4% | 16.5% |
| Semi-moist | 30% | 28% | 12% | 40.0% | 17.1% |
Many cat foods are high in protein on a dry matter basis whether they are wet or dry. The difference between wet and dry shows up more in calories per gram and in the amount you feed than in nutrient concentration. For feeding amounts, see our guide to how much wet food a cat should eat.
Reading a label in five minutes
- Find moisture, protein, fat and fibre.
- Subtract moisture from 100 to get dry matter.
- Convert each nutrient with the formula.
- Compare the two foods side by side.
- Check for a statement that the food is complete and balanced for the life stage.
If you do this for two or three foods once, you will develop a feel for what is normal, and a surprising number will turn out to be similar.
When dry matter basis is not the right tool
- For calories. Use the energy figure, or estimate it with the calorie tools.
- For minerals in prescription diets. Vets may specify limits on an as-fed or dry matter basis, so follow their advice.
- For comparing prices. Use price per 1,000 kcal.
- For judging whether a food suits your pet. Ask your vet.
- For ingredient quality. The percentages do not tell you the source or digestibility.
Quick summary
- Labels show nutrients as fed, water included, so wet and dry foods cannot be compared directly.
- Dry matter nutrient % = label % ÷ (100 − moisture %) × 100.
- A wet food at 78% moisture and 8% protein has 36.4% protein on a dry matter basis; a kibble at 10% moisture and 26% protein has 28.9%.
- Dry matter basis measures concentration, not quality; the food must be complete and balanced.
- Compare cost by price per 1,000 kcal, not by bag price.
- Use the Dry Matter Basis Calculator and read our guides on why wet food looks low in protein and how to calculate protein on a dry matter basis.
Frequently asked questions
What does dry matter basis mean?
It means a nutrient is expressed as a share of the food with the water taken out, so foods with different moisture levels can be compared on equal terms.
How do I convert a label to dry matter basis?
Dry matter nutrient % = label nutrient % ÷ (100 − moisture %) × 100. For example 8% protein in a food with 78% moisture is 8 ÷ 22 × 100 = 36.4%.
Why is dry matter basis needed?
Labels show nutrients as fed, including the water. A food that is mostly water looks low in every nutrient, even if it is rich once the water is ignored.
Is a higher dry matter percentage always better?
No. It is a fair comparison tool, not a quality score. A food must be complete and balanced for the pet's life stage, and your vet may advise a specific diet.
Does dry matter basis tell me the calories?
No. Calories need the energy value of the food, in kcal per kg, or an estimate from protein, fat and carbohydrate, which the dog food calorie calculator provides.
Can I use dry matter basis for cat food too?
Yes. The arithmetic is the same for dogs and cats and for any pet food that lists moisture and nutrients on the label.
Where do I find moisture on the label?
Look in the guaranteed analysis for maximum moisture. If it is missing, ask the maker; wet foods are often about three quarters water.
Sources
- WSAVA Global Nutrition Guidelines
- NRC (2006) Nutrient Requirements of Dogs and Cats, National Academies Press
- Pure arithmetic: dry matter % = 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 Energy ConverterConvert pet food energy between kcal per kg, per 100 g, per pound and per ounce.
- Pet Food Price per 1,000 kcal CalculatorCompare two foods fairly by price per 1,000 calories instead of price per bag.
Keep reading
- 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 to Calculate Protein on a Dry Matter BasisStep-by-step protein on a dry matter basis for dog and cat food: the formula, a conversion table for common moisture levels and worked examples.
- How Many Calories Does a Dog Need? RER, MERLearn how to calculate a dog's daily calories with RER and MER, see every life stage factor, a calorie table by weight and how to adjust the result.