Wet food or dry food?

Almost every difference starts with water

A tray of wet food is mostly water, usually somewhere between 75 and 85 percent of what is in it. A bag of kibble is dried to around 8 to 12 percent. That single fact drives most of the practical differences between the two, and it is also the reason so many wet against dry comparisons go wrong before they start.

The nutrient percentages on a pack are declared as fed, meaning they describe the product in the state you buy it. When one product is four fifths water and the other is almost none, those percentages are being measured against completely different baselines. Reading them side by side is a bit like comparing the strength of coffee by looking at the size of the mug.

Comparing on a dry matter basis

The fix is a small piece of arithmetic. Take the declared percentage, divide it by 100 minus the moisture percentage, and multiply by 100. That gives the figure on a dry matter basis, which is what the food would look like with the water taken out, and it puts both products on the same footing.

Take a wet food declaring 8 percent protein at 80 percent moisture. Eight divided by twenty, times one hundred, is 40 percent protein on a dry matter basis. Now take a dry food declaring 28 percent protein at 10 percent moisture. Twenty eight divided by ninety, times one hundred, is about 31 percent.

Read straight off the packs, the dry food appears to have three and a half times the protein. Read correctly, the wet food is the higher protein product by a comfortable margin. The same conversion applies to fat, fibre and ash, and it is the only honest way to compare across formats.

This is not a trick that favours wet food. It works in both directions, and plenty of wet foods look thin once the water is removed. The point is that you cannot tell which case you are looking at until you do the conversion.

Our pet food calculator does this conversion for two foods side by side.

Why the portions look nothing alike

Dry food generally provides somewhere around 3,300 to 4,200 kcal per kilogram. Wet food is often closer to 700 to 1,200. Per gram, that makes dry food three or four times as energy dense, and it explains why the two feeding guides look like they belong to different animals.

A cat needing about 250 kcal a day might eat roughly 65 g of a dry food at 3,800 kcal per kilogram. The same cat fed a wet food at 850 kcal per kilogram needs close to 300 g, which is three and a half 85 g pouches. Households moving from dry to wet often feed one or two pouches because that looks like a meal, and then wonder why their cat is hungry and losing condition.

If you want the full method for turning a calorie figure into a portion, that is covered in our guide on how much to feed a dog or cat. The short version is that you cannot skip the energy density.

Water intake, and why cats come up more often

Cats descend from desert animals and have a weak thirst response relative to their needs. Left with dry food and a bowl of water, many do not drink enough to fully make up the difference, so their total water intake ends up lower than a cat eating wet food.

That is why wet food comes up so often in veterinary conversations about feline urinary problems. Increasing water intake is a recognised part of managing several lower urinary tract conditions, and food is a reliable way to deliver water to an animal that will not drink on request.

It is worth being careful about how far that goes. Raising water intake is a management tool used under veterinary guidance for specific diagnosed problems. It is not a reason to assume every cat needs wet food, and it is not a substitute for seeing a vet about straining, blood in the urine, or a cat that cannot pass urine, which is an emergency.

Does dry food clean teeth?

Barely, if at all. The mental image is a kibble scrubbing the tooth as it is chewed, but most ordinary pieces shatter on first contact rather than sweeping the surface, and much of dental disease sits at and below the gum line where food never reaches.

Some products genuinely do better. Dental diets built with a larger, more fibrous kibble that shears rather than crumbles can reduce plaque and tartar, and the Veterinary Oral Health Council awards a seal to products whose manufacturers have submitted evidence for exactly that. The seal is the useful signal, because it belongs to individual products rather than to a whole format.

So dry food is not a toothbrush, and neither is wet food a cause of dental disease by itself. Brushing and veterinary dental care do the work that food cannot.

The label check that outranks the format

The most consequential thing on either pack is not whether it is wet or dry. It is whether the product is a complete food or a complementary one. Under EU Regulation 767/2009 those are defined categories: a complete feed is intended to meet all of an animal's nutritional needs on its own, and a complementary feed is not.

Complementary products are common, and they are entirely legitimate. Many pouches, trays, gravies and toppers are sold as complementary because they were designed as part of a diet rather than the whole of it. The problem only appears when a complementary food quietly becomes the main meal, because nothing in the recipe is holding the nutrient profile together.

The wording is on the pack, usually in smaller print than the flavour. Our guide to complete and balanced statements goes through where to find it and what it does and does not promise.

• Look for the words complete or complementary, and the life stage they apply to.
• Check that the life stage matches your pet, since adult and growth formulations differ.
• Treat gravies, toppers and most single pouches as extras until the label says otherwise.

Cost per calorie, and life after opening

Because you are buying water, wet food costs considerably more per calorie than dry, and the gap widens with the size of the animal. For a large dog, an all-wet diet is a serious budget decision rather than a preference. For a 4 kg cat it is far more manageable.

Storage differs too. Opened wet food needs refrigerating and using inside the window printed on the pack, and anything left in the bowl should not sit out for hours. Dry food keeps for much longer but is not indefinite: once the bag is open, fat begins to oxidise, which costs palatability and degrades some vitamins. Keeping it sealed in its own bag, out of heat and light, does more than decanting it into a bin.

Mixed feeding avoids most of the trade-offs and is common for good reason. Count the calories from both halves against one daily total, and make sure the majority of the diet comes from something labelled complete. Handling and storage are covered in more detail in our guide to recalls and safe handling.