A pate at 78 percent moisture and a kibble at 10 percent moisture are not 7 times apart in protein. They are 22 percent and 90 percent dry matter, and the guaranteed analysis printed on both bags is measured as fed, water included. Move both onto a dry matter basis and the canned food often wins by 10 points. The whole job is 2 steps and about 40 seconds on a phone calculator.
Step 1: dry matter is 100 minus moisture
Dry matter (DM) is everything that is not water. A can labeled 78 percent moisture is 22 percent DM: 100 − 78 = 22. A bag at 10 percent moisture is 90 percent DM: 100 − 10 = 90. A gravy pouch at 82 percent moisture is 18 percent DM. A freeze-dried food at 5 percent moisture is 95 percent DM. That single subtraction is the entire first step, and it is the step most people skip when they compare a 10 percent protein can to a 32 percent protein bag and conclude the bag is 3 times meatier.
Step 2: divide by DM, multiply by 100
The conversion for any nutrient is the same: DM percent = (as-fed percent ÷ DM percent) × 100. A canned food with 10 percent crude protein as fed becomes 10 ÷ 22 × 100 = 45.5 percent protein on a dry matter basis. A dry food with 32 percent protein as fed becomes 32 ÷ 90 × 100 = 35.6 percent. Fat works the same way: 6 percent fat as fed in that can is 6 ÷ 22 × 100 = 27.3 percent fat DM, against 15 ÷ 90 × 100 = 16.7 percent for the kibble. Phosphorus converts too, and that is where the arithmetic starts to matter clinically: 0.15 percent phosphorus as fed in a 22 percent DM can is 0.68 percent DM, roughly 4 times the 0.18 percent DM that a renal diet is built around.
| Food | Moisture | DM | Protein as fed | Protein DM |
|---|---|---|---|---|
| Pate can | 78% | 22% | 10.0% | 45.5% |
| Gravy pouch | 82% | 18% | 8.0% | 44.4% |
| Standard kibble | 10% | 90% | 32.0% | 35.6% |
| Semi-moist pouch | 25% | 75% | 25.0% | 33.3% |
| Freeze-dried raw | 5% | 95% | 45.0% | 47.4% |
Read the table sideways: the 2 canned formats and the freeze-dried food all land between 44 and 47 percent protein DM, while the 2 shelf-stable formats sit near 34 percent. The label numbers ranged from 8 to 45. The dry matter numbers ranged from 33 to 47. That is the entire argument for doing the division.
Error 1: comparing as-fed to as-fed
This is the default mistake, and marketing text depends on it. A can that reads 10 percent protein next to a bag that reads 32 percent looks like a 3-to-1 loss for the can. On DM it is a 45.5 to 35.6 win. The same trap runs the other way with carbohydrates: a kibble at 40 percent carbohydrate as fed is 44 percent DM, while a pate at 4 percent as fed is 18 percent DM. Neither number is good or bad on its own; the point is that the comparison only exists after both are converted.
Error 2: dividing by moisture instead of DM
People who half-remember the formula sometimes divide by the moisture figure. A 10 percent protein can at 78 percent moisture then becomes 10 ÷ 78 × 100 = 12.8 percent, which is not a real quantity and flatters nothing. The denominator is the solid fraction, never the water fraction. A related slip is subtracting moisture twice, once to get DM and again before dividing, which turns a 22 percent DM can into a 4.8 percent protein figure that would make any food look empty.
Error 3: mixing maximums with typicals
Guaranteed analysis uses minimums for protein and fat and maximums for fiber and moisture. Those are legal floors and ceilings, not measurements. Two bags both claiming 32 percent protein minimum can differ by 3 to 5 points in the lab, and a can claiming 78 percent moisture maximum may test at 76. Convert the guaranteed numbers for a quick comparison, then convert the manufacturer's typical analysis, which is usually published on request, before you make a decision worth 40 dollars a month. Never divide a minimum from one food by the DM of another.
Check 1: the components should sum to 100
Add the DM percentages of protein, fat, fiber, ash and nitrogen-free extract. A complete food lands within about 2 points of 100. If the sum reaches 108, the moisture figure is understated or the maxima are inflated; if it lands at 88, a nutrient is missing from the label. This 10-second sum catches most transcription errors before they reach a feeding decision.
Check 2: convert calories and phosphorus, not just protein
Protein gets all the attention, but the numbers that change veterinary decisions are phosphorus and calorie density. A 85 g can at 78 percent moisture holds about 18 g of dry matter and, at 75 kcal per 100 g, around 64 kcal. A 100 g of kibble at 4,000 kcal per kg holds 400 kcal. Feeding 240 kcal a day therefore means roughly 3.7 cans or 60 g of kibble, and the phosphorus load per 100 kcal, not per 100 g, is the figure to compare. The water side of that trade is worked through in wet versus dry food.
What dry matter still will not tell you
DM conversion compares composition, not quality. It cannot separate a 45 percent protein can built on muscle meat from one built on connective tissue and pea protein, and it says nothing about digestibility, amino acid balance or the 3 to 6 weeks a food has spent in a warehouse. Treat the converted number as the entry ticket to a comparison, not the verdict. If you are weighing a therapeutic diet against a grocery one, the next step is the daily volume math in how much wet food a cat needs, and an ingredient check against the toxic food list before anything new goes in the bowl.
Do this before you buy
- Write down moisture, protein, fat and phosphorus as fed from both labels.
- Subtract moisture from 100 for each food, and keep 2 decimals if the label allows.
- Divide each nutrient by its own DM figure and multiply by 100.
- Sum the converted components; if the total is off 100 by more than 2 points, stop and re-read the label.
- Compare phosphorus per 100 kcal, not per 100 g, then check the price per 100 kcal.
Terms mentioned in this article
Frequently asked
Is dry matter the same as dry food?
No. Dry matter is a calculation, not a format. Any food, including an 82 percent moisture pouch, has a dry matter figure, and that figure is what you divide by to compare nutrients across formats. Dry food simply happens to be about 90 percent dry matter, which is why its as-fed numbers sit close to its dry matter numbers.
Why does my canned food look lower in protein than kibble?
Because the label reports protein with the water still in it. A can at 78 percent moisture and 10 percent protein as fed is 45.5 percent protein on a dry matter basis, which is higher than most kibble. The label is not lying; it is answering a different question than the one you are asking.
Do I need to convert carbohydrates too?
Yes, if you are comparing carbohydrate load. Carbohydrate is rarely printed, so estimate it by subtracting protein, fat, fiber, ash and moisture from 100 on an as-fed basis, then divide that result by the dry matter figure. A 4 percent as-fed figure in a 22 percent DM can becomes 18 percent DM.
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