Wet food is mostly water, and that is the whole argument. A pate-style can holds 75–80% moisture; kibble holds 6–10%. For a cat built to draw water from prey, that gap is not a texture preference. It decides whether the bladder dilutes waste or sits in concentrated urine for eighteen hours at a stretch.
The water arithmetic decides the ratio
A healthy adult cat needs roughly 40–60 ml of water per kilogram of body weight per day, counting the water already inside food (the daily volume is worked out in how much water a cat needs). A 4.5 kg cat therefore needs about 180–270 ml a day. On dry food alone that cat drinks perhaps 60–100 ml and takes another 10–20 ml from the kibble, so it finishes the day 100 ml or more below the low end. The shortfall is quiet. Cats concentrate urine efficiently and show nothing until crystals, sludge or a blockage appear.
Flip the same cat to all wet. Two 85 g cans at 78% moisture deliver about 130 ml with the meal, and most cats lap another 30–60 ml on top. The target is met without a fountain, a broth or a syringe.
What 100% wet asks of you
All-wet feeding is the cleanest way to close the water gap and the most demanding to run. At 70–80% moisture a 4.5 kg cat eats 200–250 g a day, split across 3–4 meals, because a stomach full of wet food is a small calorie load and cats handle small meals better. Food goes down for 20–30 minutes and comes up. An opened can must be refrigerated within 2 hours and used within 24–48 hours.
Cost multiplies first. Per calorie, wet food runs roughly 1.5–3 times dry, so a cat eating 240 kcal a day costs visibly more each month. That is the honest trade: you are buying water, protein quality and palatability, and paying for the tin and the shipping weight.
Half and half is where most households land
A 50/50 split by calories, not by volume, is workable and cheaper, and it is the middle of the range covered in wet versus dry food. Wet in the morning and evening, a measured portion of dry left out for the day. The water gain: 100 g of wet at 78% moisture gives 78 ml, and 30 g of dry gives 2–3 ml plus whatever the cat drinks. You recover 70–80 ml of the gap at roughly half the cost of all-wet.
Split by calories or the ratio drifts badly. Wet food runs 70–90 kcal per 100 g and dry runs 350–420 kcal per 100 g, so equal gram weights are nowhere near equal calories. Weigh both portions for the first two weeks, then check monthly.
Four ratios, one table
| Plan | Wet share of calories | Water from food (4.5 kg cat) | Meals per day | Cost vs dry only |
|---|---|---|---|---|
| All wet | 100% | 130–160 ml | 3–4 | 1.5–3x |
| Half and half | 50% | 75–85 ml | 2–3 | 1.3–1.8x |
| Wet topper | 20–25% | 35–45 ml | 2 | 1.1–1.2x |
| Dry only | 0% | 10–20 ml | 2 | 1x |
The dental argument does not survive a close look
"Dry food cleans teeth" is the most repeated and least supported claim in cat feeding. Kibble shatters against the carnassial teeth and the crumbs fall away; many cats swallow pieces whole without chewing at all. The 1–2 mm of contact sits on the crown, not at the gumline where periodontal disease starts, and cats fed dry food show plaque and gingivitis at rates similar to cats fed wet.
What does work: brushing with a pet enzymatic paste 3–7 times a week, a dental diet carrying a VOHC seal, or a chlorhexidine gel applied to the outer tooth surfaces. If you keep dry food, keep it for convenience and cost, not for teeth.
Wet food earns a genuine point on the other side. Higher water intake dilutes urine, which lowers the risk of struvite and calcium oxalate crystals and helps cats with chronic kidney disease (CKD) or a history of blockage. On the urinary question the trade favors wet, clearly.
Spoilage: the 2-hour rule
Wet food is a bacterial culture medium at room temperature. Put down only what the cat finishes in 20–30 minutes, then lift the bowl. Anything left out beyond 2 hours goes in the bin, never back in the fridge. An opened can keeps 24 hours at 4°C and 48 hours at the outside. Above 27°C indoors, cut the floor time to 15 minutes and the fridge life to one day.
Signs a can has turned: sour or metallic smell, a bulging lid, foam at the rim, or a cat that sniffs and walks away from food it normally attacks. Throw it out. A single bout of food poisoning costs more than the can. A dented seam or a pull-tab that hisses on opening is also suspect; do not test it on the cat.
Transition ratios and soft stool
Moving to wet is a diet change, and the gut needs 7–14 days, and the schedule below follows the general method in how to switch cat food. A common approach: 25% wet by weight for 3 days, 50% for 3 days, 75% for 3 days, then full. If stool softens, hold at the last good ratio for 3–4 days before continuing.
Soft stool in week one usually means one of three things: too fast a transition, too much fat in the new food, or a sudden drop in fiber. Add 1 teaspoon of plain canned pumpkin per 5 kg of cat, or simply slow down. Loose stool that lasts beyond 48 hours, contains blood or mucus, or arrives with vomiting or a cat that stops eating is a vet visit, not a ratio problem. Serve food at room temperature or 30–35°C; cold food smells like nothing and cats refuse it.
Five steps for this week
- Weigh the cat, multiply by 40–60 ml/kg, and write the daily water target on the fridge.
- Pick a ratio: all wet if the budget allows, 50/50 by calories if not, 20–25% as the floor for a cat that refuses more.
- Weigh both portions in grams for 14 days, then switch to a marked scoop and recheck monthly.
- Set two rules: bowl up after 25 minutes, opened cans into the fridge within 2 hours.
- Book a dental check and start brushing 3–7 times a week. Kibble will not do that job.
Frequently asked
Is it bad to feed wet food and dry food at the same meal?
Mixing them in one bowl is safe but wasteful of the dental and textural benefit, and it makes portion control harder because the two foods have very different calorie density. Feed wet as a timed meal and dry as a measured portion at a separate time, at least 30 minutes apart. Cats that bolt wet food and then vomit often do better with the two separated, and cats on a weight plan need the split so the dry portion can be counted to the gram.
Does all-wet feeding cause diarrhea in cats that are used to kibble?
Not by itself, but a fast switch will. Wet food carries 70–80% water and usually more fat than kibble, so a cat moved overnight from dry to wet often produces soft stool for two or three days. Move in steps of 25% by weight every three days, hold at the last firm-stool ratio if it softens, and see a vet if loose stool lasts past 48 hours or comes with vomiting, blood or a cat that stops eating.
How long can an opened can of wet food stay in the fridge?
Twenty-four hours is the safe target and 48 hours is the outside limit, stored at 4°C in a lidded container rather than the bare can. Food left on the floor past 2 hours at room temperature should be discarded, not refrigerated. Serve it at room temperature or warmed to 30–35°C, because cold food releases almost no aroma and many cats will refuse a bowl that smells like nothing at all.