Dry Matter Calculator: the simple way to compare pet foods accurately
Pet food labels list nutrients on an “as-fed” basis, which includes water. That makes a can and a kibble look wildly different even when the actual nutrition is similar. A dry matter calculator removes moisture from the math so protein, fat, fiber, ash, and carbohydrates can be compared fairly. This guide explains the formula, shows examples, and walks through best practices so every comparison feels clear and confident.
What is dry matter (DMB)?
Dry matter expresses nutrients after removing water. It answers a simple question: “What percent of this food is protein, fat, fiber, ash, and carbohydrates once moisture is out of the way?” Because water content swings from ~8–12% in kibble to ~70–80% in many canned foods, as-fed percentages can mislead. Dry matter puts every product on the same playing field.
Think of two sponges—one soaked, one dry. They’re the same sponge, yet the wet one weighs more and looks “bigger.” Pet foods behave the same way when water is included in the math. Dry matter strips away that distortion.
Why dry matter comparisons matter
- Fair comparisons across formats. Wet, semi-moist, air-dried, and kibble can be compared with one standard.
- Clarity for special diets. Veterinary diets often target protein, fat, fiber, or carbohydrate ranges. Dry matter tells whether a product really fits.
- Better conversations with the vet. Numbers mean the same thing to everyone when moisture is normalized.
- Smarter brand switching. Ingredient lists vary; nutrient density on a dry-matter basis reveals the real differences.
The dry matter formula
The conversion is straightforward. For any nutrient listed on the label as a percentage on an as-fed basis:
Label values
Protein, fat, fiber, ash (as-fed %)
Moisture (as-fed %)
Dry matter formula
DMB% = As-fed% × 100 ÷ (100 − Moisture%)
Remove water from the math by dividing by the dry portion.
Result
Protein, fat, fiber, ash, carbs (DMB %)
Moisture comes directly from the guaranteed analysis panel on the label. If a range is given, use the typical value or ask the manufacturer for the average. Many brands will share typical moisture on request.
How to use the Dry Matter Calculator
- Collect the guaranteed analysis. Grab protein, fat, fiber, moisture, and ash if listed. If ash is missing, leave it blank.
- Enter the numbers on an as-fed basis. Use the exact percentages from the label.
- Get instant dry-matter values. The calculator applies the formula to each nutrient.
- Let “Others” auto-calculate. Others represents carbohydrates plus any remaining constituents not listed. When ash is entered, Others becomes carbohydrates by difference.
- Compare two products side by side. Toggle compare mode to see clean, readable tables for both products.
Input fields you’ll need
- Protein (as-fed %)
- Fat (as-fed %)
- Fiber (as-fed %)
- Moisture (as-fed %)
- Ash (as-fed %, optional) — include it when the label provides it.
Result fields you’ll see
- Protein, Fat, Fiber, Ash (DMB %) — each normalized for moisture.
- Others (DMB %) — carbohydrates plus any remaining components.
- Sum* — total of all dry-matter values. Slight drift from 100% can occur due to rounding on labels.
Worked example: wet food vs kibble
Here’s a simple, transparent example that mirrors what the calculator does behind the scenes.
Convert to dry matter:
- Wet food protein DMB = 9 × 100 ÷ (100 − 78) = 40.9%
- Kibble protein DMB = 26 × 100 ÷ (100 − 10) = 28.9%
On the label the kibble looks “higher protein,” yet on a moisture-free basis the wet food actually carries more protein per gram of dry matter. The same approach works for fat, fiber, and ash.
Carbohydrate by difference
Pet food labels in many regions don’t list carbohydrates directly. They can be estimated by difference:
Carbohydrate (as-fed) = 100 − Protein − Fat − Fiber − Ash − Moisture
The calculator uses that same logic for Others on an as-fed basis, then converts it to a dry-matter value just like the other nutrients. When ash is not provided, Others includes ash and carbohydrates together. When ash is provided, Others reflects carbohydrates more closely.
Reading labels without guesswork
Guaranteed analysis values are minimums or maximums, not exact points. Protein and fat appear as minimums. Fiber and moisture appear as maximums. Ash may appear as a maximum or may not appear at all. That labeling style allows real products to vary slightly while staying compliant.
Because of that policy, summed dry-matter values may land a hair above or below 100%. A small gap is normal. Large gaps point to missing inputs or a typo. When in doubt contact the brand for typical analysis values.
Moisture targets by format
- Dry kibble: often 8–12% moisture
- Semi-moist or air-dried: commonly 12–30%
- Canned: frequently 70–80%
These are not rules. They’re practical ranges that make label reading easier. Products can sit outside these ranges and still be great choices. Dry matter keeps the math honest.
Common mistakes to avoid
- Using the wrong moisture. Always use the moisture percentage from the same label panel as the other nutrients.
- Forgetting ash when it’s listed. If ash appears on the label, include it. The carbohydrate estimate grows more accurate.
- Converting twice. If a brand already presents dry-matter numbers in a brochure, don’t run them through the formula again.
- Comparing different serving bases. Stick with percentages by weight for DMB. “Per cup” or “per can” comparisons require a different approach.
Frequently asked questions
How do you convert as-fed to dry matter?
Multiply the as-fed percent by 100, then divide by 100 minus the moisture percentage. That’s it. This method is used widely in veterinary nutrition and feed science.
Why do sums not equal 100% exactly?
Labels use minimums and maximums. Rounding creates small gaps. Manufacturing tolerances also create slight variation. Differences of one or two percentage points are common and not a sign of a problem.
Is a higher dry-matter protein always better?
Not always. Protein quality, amino acid balance, digestibility, energy density, and a pet’s specific needs all matter. A puppy needs different nutrition than a senior cat. Dry matter helps compare like for like yet it does not replace professional advice.
How do carbs appear if they’re not listed?
Carbohydrates are estimated by difference after subtracting protein, fat, fiber, ash, and moisture from 100 on an as-fed basis. The result then converts to a dry-matter percentage with the same formula.
What if the label does not show ash?
Leave ash blank. Others will include ash and carbohydrates together. If ash later becomes available, enter it and the calculator will update the carbohydrate estimate automatically.
Do dry-matter values apply to treats?
Yes, the math still works. Use the guaranteed analysis on the treat package. Dry matter will show nutrient density per unit of dry material just like it does for complete diets.
Authoritative resources
For readers who want deeper background on label rules, nutrient conversions, and clinical feeding, these are trusted starting points:
- Merck Veterinary Manual — broad veterinary reference that covers nutrition and labeling basics.
- WSAVA Global Nutrition Guidelines — guidance on evaluating foods and discussing nutrition with owners.
- AAFCO — model regulations for pet food labeling in the United States.
- FEDIAF — European pet food industry guidelines and nutrient recommendations.
Quick reference: dry matter conversion at a glance
| Step | Action | Example |
|---|---|---|
| 1 | Collect as-fed % and moisture % from the label | Protein 9%, Moisture 78% |
| 2 | Apply the formula to each nutrient | 9 × 100 ÷ (100 − 78) = 40.9% |
| 3 | Estimate carbohydrates by difference if desired | Others AF = 100 − protein − fat − fiber − ash − moisture |
| 4 | Convert Others to dry matter with the same formula | Others DMB = Others AF × 100 ÷ (100 − moisture) |
Pro tips for fast, accurate comparisons
- Photograph labels. A clear photo of the guaranteed analysis prevents retyping errors.
- Use the same units. Percent by weight is standard for DMB. Avoid “per cup” mixes while comparing DMB values.
- Record ash when available. Carbohydrate by difference becomes more precise.
- Check energy density later. Dry matter describes composition. Calories (ME) describe energy. Both matter for feeding plans.
When to talk with a veterinarian
Dry matter helps compare products. It does not diagnose or treat conditions. For chronic issues like kidney disease, pancreatitis, obesity, allergies, or IBS, a veterinarian can interpret dry-matter numbers in the context of the full diet and the pet’s medical history. When a pet needs a therapeutic diet, follow the prescribing veterinarian’s guidance.
Add this calculator to a nutrition workflow
- Shortlist three foods that meet life-stage and AAFCO or FEDIAF statements.
- Convert each label to dry matter with the calculator.
- Compare protein and fat first. Check fiber next. Review carbohydrate if relevant.
- Check calories per 100 g or per cup. Ensure the feeding guide fits the pet’s energy needs.
- Pick the best match based on nutrition, ingredient sourcing, budget, and availability.
Key takeaways
- Dry matter removes water from the equation so comparisons are fair.
- The formula is simple: DMB% = As-fed% × 100 ÷ (100 − Moisture%).
- “Others” equals carbohydrates plus any remaining constituents after protein, fat, fiber, ash, and moisture.
- Small rounding differences are normal because labels use minimums and maximums.
- Use dry matter for composition, then check calories to complete the picture.
