Why cost per kilo is the wrong way to compare pet food

Why cost per kilo is the wrong: Cost per kilo is the price of a food divided by its weight, and it is the figure almost everyone uses to decide whether a pet food is expensive. It is also the figure most likely to mislead. The reason is simple once stated: a dog or cat does not eat kilos, it eats calories, and two foods with the same price per kilo can deliver very different amounts of nutrition per serving. The honest unit of comparison is cost per meal, sometimes expressed as cost per day, worked out on the ration actually served. This article shows why the popular metric breaks down and how to replace it with one that holds up. Note that Petipedia quotes no retail prices and holds no commercial relationships: this is about method, not products.

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The hidden variable: energy density

Energy density is how many calories a food packs into a given weight, usually stated as kilocalories per 100 grams. It is the variable that quietly governs how much you pour, and therefore how fast the bag empties. A more energy-dense food is eaten in smaller portions, so even at a higher price per kilo it can cost less per meal. The effect is not marginal. A density gap of only 100 kilocalories per 100 grams can be enough to reverse the price-per-kilo ranking, which is exactly why an isolated price per kilo misleads (WSAVA, 2021).

This is why the WSAVA advises assessing intake on an energy basis, in grams per 1,000 kilocalories, rather than by weight sold (WSAVA, 2021). The energy basis neutralises both the water in wet food and the density differences between dry foods, putting genuinely comparable products side by side.

A worked comparison

Consider two dry foods. Food A looks cheaper per kilo, Food B looks pricier. Translate each into what a dog actually needs in a day, and the ranking can invert.

Because Food B is denser, the dog eats noticeably less of it each day. Two kibbles at the same price per kilo can show a very different cost per meal depending on their energy density, and the denser one frequently wins on the only metric that matters to your wallet over a month (WSAVA, 2021). The price per kilo told you nothing useful on its own.

Wet food makes the trap worse

Format magnifies the distortion. Wet food carries a far higher cost per calorie than dry food, because so much of its weight is water. In France, dry food made up 847,500 of the 1,194,000 tonnes sold in 2024 and wet food 320,500 tonnes (FACCO, 2024), yet a wet-led cat budget behaves very differently from a dry-led one precisely because of that cost-per-calorie gap. Comparing a wet food and a kibble by price per kilo is close to meaningless: you are partly comparing the price of water. Reasoning in grams per 1,000 kilocalories is the only way to neutralise the misleading effect of moisture (WSAVA, 2021).

How to calculate cost per meal

The method is short and needs only the bag and a kitchen scale. First, find the food's energy density in kilocalories per 100 grams, which premium foods state on the pack. Second, work out your pet's daily calorie need, or read the daily grams from the feeding chart as a starting point and adjust to body condition. Third, weigh the real daily portion rather than scooping by volume. Fourth, multiply the daily grams by the price per gram to get cost per day, and multiply by 30 for a monthly figure. The reliable unit stays the cost per day, worked out on the real ration (WSAVA, 2021).

A few practical refinements keep the figure honest. Treats belong in the budget, kept within the recommended 10 percent of caloric intake, and any supplements add to the total (PMC, 2024). And the portion that counts is the one your pet actually needs at a healthy weight, not the generous figure on the bag, because overfeeding inflates both the cost and the waistline.

The grams-per-1,000-kcal yardstick

If cost per meal is the practical metric, grams per 1,000 kilocalories is the precise one, and it is worth understanding because it neutralises every distortion at once. The idea is to express how much food delivers a fixed amount of energy, so water content and density both drop out of the comparison. A denser food needs fewer grams to hit 1,000 kilocalories; a wet food needs far more, because much of its weight is water. The WSAVA recommends exactly this basis, advising owners to reason in grams per 1,000 kilocalories rather than by weight sold (WSAVA, 2021). Once two foods are expressed this way, you can multiply by their respective price per gram and get a like-for-like cost of energy, which is the only thing the animal is actually buying when it eats.

Body size scales the stakes

The size of your animal decides how much any of this matters to your budget. Public benchmarks put the annual food spend of a 30 kilogram (66 pound) dog at roughly three to four times that of a 5 kilogram (11 pound) dog on a comparable diet (Woopets, consulted 2026), because larger animals simply eat more energy. For a large dog, a small error in the cost-per-meal calculation is multiplied across a large daily ration and a long year, so getting the metric right is worth real money. For a small dog or a cat the absolute spend is lower, but the same denser-is-cheaper logic still holds. The market context reinforces the point: French manufacturers sold 1,194,000 tonnes of pet food in 2024, of which 847,500 tonnes were dry and 320,500 tonnes wet (FACCO, 2024), and premiumisation and humanisation continue to drive the growth of wet food and treats across the US, UK and EU (FACCO, 2025). More owners are moving towards the format where price per kilo misleads most.

Concentration has a second dividend

There is a quiet bonus to a more energy-dense, highly digestible food that never shows up in either price metric. Because more of the food is absorbed, less passes through, which tends to mean smaller and firmer stools and less waste per feeding. A food that is digested efficiently delivers more of what you paid for to the animal rather than to the litter tray or the garden. This is not a reason to chase density blindly, since the food still has to suit the individual and its life stage, but it is a reminder that the cheapest-looking bag on the shelf and the best value over a month are frequently different products, and that digestibility, like energy density, is invisible in a price-per-kilo figure.

Alt text: "Bar comparison of two pet foods ranked oppositely by price per kilo and by cost per meal, with energy density marked as the reason for the reversal."

Why the wrong metric is so sticky

Price per kilo is sticky because it is printed for you, requires no arithmetic, and feels objective. It also flatters the cheaper-looking bag, which is comforting at the shelf. The trouble is that it answers the wrong question. It tells you the price of carrying the food home, not the price of feeding the animal, and those two numbers can rank foods in opposite orders. Any value comparison that stops at price per kilo is, in effect, comparing packaging weights.

When the cheaper-looking bag really is cheaper

To be fair to the simple metric, price per kilo and cost per meal do sometimes agree. If two foods have similar energy density and similar moisture, the one with the lower price per kilo will usually also be cheaper per meal, and the shortcut holds. The trouble is that you cannot know whether you are in that lucky case without checking the energy density, so the only safe habit is to check every time. The cost of checking is one multiplication; the cost of not checking is potentially months of overpaying or overfeeding. A quick worked example shows the stakes. Suppose a dog needs 700 kilocalories a day. On a 350 kilocalorie per 100 gram food it eats 200 grams daily, or 6 kilograms a month; on a 450 kilocalorie food it eats about 156 grams, or 4.7 kilograms a month. That denser food can cost noticeably more per kilo and still empty the bag more slowly, which is the entire point: the bag you replace less often is frequently the better deal, and the shelf price alone will never tell you which one that is.

A note on overfeeding and the budget

One distortion sits upstream of every calculation: the portion you actually serve. If you feed to the generous figure on the bag rather than to the animal's real need at a healthy weight, you inflate the monthly cost and the waistline together. The most expensive feeding mistake is not choosing the pricier food, it is serving too much of any food. Anchoring the cost-per-meal sum on a correctly sized portion, weighed rather than scooped, is therefore both a budget tool and a health one, and the two interests point the same way for once.

Where to go next

The full reasoning on relative cost and value, including cost per day worked through different body sizes, sits in our budget and value FAQ, and the role of energy density in how much you actually feed is covered in the protein and macronutrients FAQ. For a structured routine you can reuse at any shelf, the cost per meal value guide turns this into a repeatable calculation, and the dry versus wet food comparison guide applies it across formats. The pivotal concept throughout is energy density, which is why two equally priced bags are rarely equally economical.

The takeaway (cost kilo)

A pet does not eat weight, it eats calories, so weight-based pricing is the wrong yardstick. Energy density decides how much you pour, a gap of only 100 kilocalories per 100 grams can reverse a price-per-kilo ranking, and water makes wet food look cheaper by the kilo than it is per calorie. Replace the printed price per kilo with a cost per meal worked out on the real ration, and the genuinely economical food often turns out to be the one that looked more expensive on the shelf.