Why We Don't Sell 5 kg Bags of Cat Food in Singapore

Published 1 August 2026 by Kopipets (Surplus Media Pte. Ltd., UEN 202448810R), Singapore. This article sets out three statements we had published on our own About page and have now corrected there, including one number we had wrong since we wrote it. Nothing here is veterinary advice.

The short version

We sell dry cat food in 1.5 kg bags. We do not sell 5 kg bags. People assume the reason is that big bags spoil in Singapore's heat, and we have said something close to that ourselves on our About page. Having gone and read the evidence properly, we no longer think that reason survives contact with the literature, and we have corrected it.

The reason that does survive is duller and more arithmetical. One average cat eats roughly 56 g of dry food a day. A 5 kg bag is therefore about three months of feeding, and a 7.5 kg bag is about four and a half. Over that span the thing that measurably changes in a bag is not fat going rancid — it is the fat-soluble vitamins declining, which happens on a timescale of months regardless of how carefully you seal it. A 1.5 kg bag is about four weeks. That is the whole argument, and it is weaker than the one we used to make.

It also has a real counter-argument, which we state in full below: big bags are meaningfully cheaper per kilogram, and if you have three cats you should buy one. We are not going to pretend otherwise.

The thing that makes this position less brave than it sounds

Before the argument, the disclosure that undercuts it.

We wrote our original About page paragraph as though declining the 5 kg bag were a stand against an industry norm. In Singapore it is not the norm. In July 2026 we went through the dry cat food listings of the large local retailers and counted what sizes they actually carry: roughly 274 dry cat food entries at Kohepets, 464 at Pet Lovers Centre, 382 at CatSmart, plus the FairPrice and Pawpy Kisses ranges. The dominant sizes across all of them sit in the 1.2 kg to 2 kg band. Bags of 10 kg and above were under five percent of what Pet Lovers Centre listed.

That count is ours, done by hand from public product listings on one date, and it is not market-share data — it is assortment, which is a different thing. A retailer can list one 1.5 kg SKU for every ten it sells. But it does mean the honest framing is not "we refuse to do what everyone else does." It is: the small bag is already mainstream here, and we declined the extra margin that a big-bag SKU would have added on top of it.

And here is the part that costs us nothing to say because it costs us nothing: a 1.5 kg bag is more expensive per kilogram for you than a 5 kg bag would be, and we are the party that benefits from that. Small bags carry better per-kilo margin almost everywhere in this industry. Any argument we make for the small bag is an argument that happens to suit us. Weigh it accordingly.

The arithmetic, which you can redo yourself

Everything below rests on one number: how much dry food a cat eats in a day. There are three independent ways to get at it and they converge.

The 2021 AAHA nutrition guidelines give resting energy requirement as 30 × body weight in kg + 70. For a 4 kg cat that is 190 kcal, multiplied by roughly 1.2 to 1.4 for a neutered indoor adult, giving about 230 to 265 kcal a day. FEDIAF's 2025 nutritional guidelines use 75 to 100 kcal per kg of metabolic body weight, which for a 4 kg cat works out at about 190 to 250 kcal. Tufts published 260 kcal for a 4.5 kg cat in 2022.

Dry cat food runs around 3,700 to 3,800 kcal per kilogram. Divide, and a 4 kg cat eats somewhere between 50 g and 70 g a day. Royal Canin's own feeding table lands at 56 g for a 4 kg cat, which is comfortably inside that band, so we will use 56 g as the worked example and give the range around it.

At 56 g a day, for one cat:

A 1.5 kg bag lasts about 27 days — call it four weeks. Range, at 50 to 70 g: 21 to 30 days.
A 5 kg bag lasts about 89 days — call it three months. Range: 71 to 100 days.
A 7.5 kg bag lasts about 134 days — nearly four and a half months. Range: 107 to 150 days.
A 10 kg bag lasts about 179 days — around six months. Range: 143 to 200 days.

Two cats halve all of those. Three cats cut them to a third: at 168 g a day, three cats finish a 10 kg bag in about 60 days, which is a perfectly reasonable open-bag life.

If your cat is heavier, lighter, unneutered, very young or unusually active, redo the sum with your own weight figure. The point of showing the method rather than just the conclusion is that you do not have to take our number for it.

What actually changes in a bag over three or four months

Here the evidence splits cleanly into a part that is well supported and a part that is not.

The well-supported part is vitamin decline. A Kansas State University thesis measuring vitamin retention in extruded pet food found fat-soluble vitamin levels falling by roughly half over six months of storage at 20 °C and 50 percent relative humidity — that is, in air-conditioned laboratory conditions, not tropical ones. Manufacturers know this and overformulate vitamin premixes against it, which is precisely why the decline is expected rather than alarming. But it is real, it is measured, and it runs on a months timescale. A bag that takes three to four and a half months to finish spends its second half further down that curve than its first half.

There is also a measured effect on the fat itself, though a more modest one than folklore suggests. Hołda and Głogowski, publishing in the Journal of Thermal Analysis and Calorimetry in 2016, tracked four dry pet foods over seven months and found the acid value rising significantly in all four. The interesting detail is which one held up best: the food with the lowest polyunsaturated fat content, at 7.5 percent, against 18 to 24 percent in the others. Fat composition mattered more than time did.

Our own food is a minimum of 15 percent crude fat, with duck oil and fish oil in the formulation. Fish oil is high in polyunsaturates. That is a reason for us specifically to prefer a bag that gets finished, and we would rather say it in those terms than as a general law about all dry food.

The claim we are not making, and the study that stopped us making it

Our About page used to say that fat "oxidises once a bag is opened to warm, humid air" and that the food "slowly goes stale." We removed it on the day this article went up, because the most directly relevant study we could find points the other way.

Park and colleagues, in Food Science of Animal Resources 45(2):504–516, 2025 (DOI 10.5851/kosfa.2024.e51), stored unsealed dry pet food at 25 °C and at 35 °C for 120 days. TBARS — the standard laboratory index of lipid oxidation — did not climb. It declined, from 3.77 to between 3.27 and 3.28. There was no microbial growth. And 35 °C is above Singapore's normal daytime maximum, so the harsher arm of that experiment was harsher than a Singapore kitchen.

You can raise objections to it. TBARS measures secondary oxidation products that can themselves degrade further, so a falling TBARS number is not the same as no oxidation at all; 120 days is not 12 months; one product is not all products; and a sealed laboratory cabinet is not a bag opened and reclosed twice a day with a scoop. Those are fair. What we do not think is fair is to go on publishing a claim on our own site while a study that directly contradicts it exists and we have read it. That is why it is no longer there.

So the honest position is: we cannot show you that kibble goes rancid in a Singapore flat. We can show you that vitamins decline over months. Those are different claims and only the second one is ours to make.

Two more things we will not say. We will not tell you that dry food grows mould in Singapore's humidity — kibble sits at a water activity of roughly 0.23, and the moulds people worry about need something in the region of 0.60 before they can do anything at all. And we will not connect any of this to feline steatitis, which in the veterinary literature is associated with diets built on fish products and inadequate vitamin E, not with a bag of complete dry food left open in a kitchen.

The rule we are not repeating either

"Use dry food within six weeks of opening" circulates widely enough that people quote it as though it came from somewhere. We went looking for the somewhere and could not find it.

The FDA's pet food storage guidance gives post-opening handling advice and refrigeration limits for canned food. AAFCO's consumer material does the same. Hill's and Texas A&M's veterinary extension material both give a three-to-five-day refrigerated limit for opened cans and no post-opening limit at all for dry. The only manufacturer figure we found for dry food is Purina's, which is two to three months — long enough that it would accommodate a 5 kg bag rather than rule one out.

We are pointing this out against our own interest. The six-week rule, if it were real, would be the single strongest argument for our position. It is not real, so we are not going to use it.

What we got wrong on our own About page

Three things, all of which we have now fixed on that page.

One: the oxidation claim. Covered above. It has come out.

Two: the arithmetic. The page said a 5 kg bag lasted "around 70 days" and a 1.5 kg bag "roughly three weeks." Both of those assume 71 g a day, which is at the very top of the plausible range and above every feeding table we checked. At 56 g the real figures are about 89 days and about 27 days. We were understating how long a big bag lasts, which flattered our own argument, and understating how long our own bag lasts, which did not. The page now carries the corrected figures.

Three: the multi-cat framing. The page dismissed multi-cat households as "a small and legally bounded group," on the basis that HDB caps flats at two cats. That premise needed a footnote. Under the fosterer pilot running from 3 August 2026 to 31 July 2028, approved fosterers may keep up to six cats in a 3-room or larger HDB flat and up to ten in private property. More importantly, using a housing rule to wave away the households for whom the big bag is correct was a rhetorical move, not an argument. Those households exist and they are right. The page now says so.

The case for the big bag, made properly

If we are going to argue against something, we should state it at full strength first.

Big bags are cheaper per kilogram, and not trivially so. Working through the Royal Canin size ladder at Pet Lovers Centre, moving from a 2 kg bag to a 10 kg bag saves somewhere between 12 and 22 percent per kilogram at list price, and up to about 28 percent when the large size is on promotion. For a 4 kg cat eating Feline Fit, that difference is on the order of S$100 a year.

The gap widens on promotion, because retailers discount the large sizes harder — we saw roughly 14 to 15 percent off 2 kg bags against 22 to 26 percent off 10 kg bags. So the person who buys big and buys on offer is not making a small saving; they are making the largest single saving available in this category.

Set against that, the cost of the small bag is a hundred dollars a year for one cat, and the benefit is that the food in the second half of the bag is closer in age to the food in the first half. We think that is a defensible trade for a single-cat household. We do not think it is an obvious one, and anyone who weighs it the other way is not making a mistake.

So who should ignore this article

Buy the big bag if you have two or more cats. At two cats a 5 kg bag is about six and a half weeks and a 10 kg bag about three months — both entirely sensible open-bag lives. At three cats a 10 kg bag is two months.

Buy the big bag if you are fostering. Under the pilot above, a fosterer with six cats is going through roughly 336 g a day, which is a 10 kg bag a month.

Buy the big bag if money is the binding constraint. A hundred dollars a year is a hundred dollars, and a cat that is fed slightly older food is in a far better position than a cat whose owner is struggling to buy food at all. We would rather say that plainly than let anyone read a nutritional warning into a decision that is really about price.

Buy the big bag if you can decant it. Splitting a 10 kg bag into sealed containers and keeping the bulk of it closed addresses part of the problem, though not the vitamin clock, which runs on time rather than on air exposure.

Where we could be wrong

Our retailer count was assortment, not sales, taken on one date in July 2026 by hand. If someone has actual Singapore sales-by-size data, it would beat our count and we would publish the correction.

The 2025 storage study is one study on one category of product over 120 days. If a longer or broader study finds oxidation climbing in tropical conditions, the rancidity argument comes back and we will say so — including that we were wrong to have withdrawn it.

The vitamin-decline data comes from storage at 20 °C and 50 percent relative humidity. Singapore is warmer and much wetter. We would expect that to make the decline faster rather than slower, but we are inferring that direction rather than measuring it, and an inference is not a measurement.

We have not measured anything ourselves here. No bag of our own food has been through a storage trial. Everything above is arithmetic over published figures, and we would rather tell you that than let the density of citations imply otherwise.

And the conflict of interest stated at the top has not gone anywhere: we sell the small bag.

Questions we get asked

How long does a 1.5 kg bag of dry cat food last one cat?
About four weeks. At 56 g a day it is 27 days; across the plausible 50 to 70 g range it is 21 to 30 days.

How long does a 5 kg bag last one cat?
About three months — 89 days at 56 g a day, and 71 to 100 days across the range. A 7.5 kg bag is about four and a half months and a 10 kg bag about six.

Does dry cat food go rancid in Singapore's heat and humidity?
We cannot show you that it does. A 2025 study stored unsealed dry pet food at 25 °C and 35 °C for 120 days and found the lipid oxidation index falling rather than rising, with no microbial growth. We used to make this claim on our own About page and we have withdrawn it.

Should I throw out dry food six weeks after opening?
There is no authority behind the six-week figure that we could locate. The regulators' post-opening limits are for canned food. The only manufacturer figure we found for dry food is Purina's two to three months.

What actually changes in an open bag, then?
Fat-soluble vitamins decline measurably over months — roughly halving over six months in one university storage study, and that was at 20 °C in dry air. Manufacturers overformulate against this, but it is the change that is actually documented.

Can dry cat food grow mould in a Singapore flat?
Not from ambient humidity alone. Kibble sits at a water activity around 0.23 and the relevant moulds need roughly 0.60. Water getting into the bag is a different matter.

Is the big bag cheaper?
Yes, clearly. Across the Royal Canin size ladder at a major Singapore retailer, going from 2 kg to 10 kg saves about 12 to 22 percent per kilogram at list price and up to 28 percent on promotion — on the order of S$100 a year for one 4 kg cat.

Who should buy the big bag anyway?
Anyone with two or more cats, anyone fostering, anyone for whom the per-kilogram price is the binding constraint, and anyone who will decant it into sealed containers. For a two-cat household a 5 kg bag is about six and a half weeks, which is a sensible open-bag life.

Sources and standards referred to

2021 AAHA Nutrition and Weight Management Guidelines for Dogs and Cats (resting energy requirement formula).
FEDIAF Nutritional Guidelines for Complete and Complementary Pet Food for Cats and Dogs, 2025 edition (maintenance energy range).
Cummings School of Veterinary Medicine at Tufts University, Petfoodology, 2022 (worked daily energy example).
Park D et al., "Effect of storage temperature on the quality of dry pet food," Food Science of Animal Resources 45(2):504–516, 2025, DOI 10.5851/kosfa.2024.e51 (unsealed storage at 25 °C and 35 °C over 120 days).
Hołda K and Głogowski R, Journal of Thermal Analysis and Calorimetry, 2016 (acid value over seven months across four dry foods of differing polyunsaturated fat content).
Kansas State University graduate thesis on vitamin retention in extruded pet food during storage (fat-soluble vitamin decline at 20 °C, 50 percent relative humidity).
US Food and Drug Administration, pet food storage and handling guidance.
Association of American Feed Control Officials, consumer guidance on pet food storage.
Texas A&M University College of Veterinary Medicine, pet food storage guidance.
Hill's Pet Nutrition, consumer guidance on storing and handling pet food.
Purina consumer guidance on dry food shelf life after opening.
Royal Canin published feeding tables (daily ration by adult body weight).
Product listings and prices at Kohepets, Pet Lovers Centre, CatSmart, FairPrice and Pawpy Kisses, counted by hand in July 2026.
National Parks Board Animal and Veterinary Service, cat licensing framework and the fosterer pilot running 3 August 2026 to 31 July 2028.

About this article

Kopipets is a Singapore pet supplies brand for cats and dogs, operated by Surplus Media Pte. Ltd. (UEN 202448810R), a Singapore-registered company and the importer of record for the products we sell. We hold our own stock in a local warehouse, inspect it on arrival, and deliver islandwide with our own vehicles.

We sell 1.5 kg bags of dry cat food and we do not sell 5 kg bags, which makes this article an argument in our own favour. We have tried to mark every point where the evidence runs against us rather than smooth it over: the six-week rule does not exist, the rancidity claim did not survive, the big bag is genuinely cheaper, and our own About page had the arithmetic wrong in the direction that suited us. If you find something here that is still wrong, write to info@kopipets.com.sg and we will correct it in public rather than quietly.

Related reading: our About page, which we have amended in line with this article; what a formaldehyde test on cat litter actually measures; and the Singapore cat licence, before the free period ends on 31 August 2026.