Everyone who owns a dog has run out of food at an awkward moment, and everyone who owns a dog has also bought a huge bag that went stale before it was finished. Both mistakes come from not knowing how long a bag lasts. The sum is simple: divide the weight of the bag by the amount your dog eats each day. But the inputs need care, because the daily amount depends on calories, not on a guess or the bag’s table. This guide shows the sum, gives a table for dogs from 5 to 30 kg and bags from 2 to 15 kg, explains freshness and storage and shows how to set a reorder reminder. Use the Pet Food Bag Duration Calculator for your own numbers.
The formula
days = bag weight in grams ÷ daily grams
Start from the dog’s daily calories (for a neutered adult, 1.6 × 70 × weight ^ 0.75) and divide by the food’s kcal per gram to get daily grams; the Dog Food Calculator does this. For a neutered 20 kg dog on a 3,600 kcal/kg food, daily grams are 294. A 10 kg bag holds 10,000 g, so it lasts 10,000 ÷ 294 = 34 days.
A table by dog size and bag size
The table assumes neutered adults and a 3,600 kcal/kg food. Days are rounded to one decimal.
| Dog | Daily grams | 2 kg bag | 5 kg bag | 10 kg bag | 15 kg bag |
|---|---|---|---|---|---|
| 5 kg | 104 | 19.2 days | 48.1 days | 96.1 days | 144.2 days |
| 10 kg | 175 | 11.4 days | 28.6 days | 57.2 days | 85.7 days |
| 20 kg | 294 | 6.8 days | 17.0 days | 34.0 days | 51.0 days |
| 30 kg | 399 | 5.0 days | 12.5 days | 25.1 days | 37.6 days |
The table makes the freshness problem plain. A 5 kg dog takes more than three months to finish a 10 kg bag, and almost five months for a 15 kg one. Makers generally advise using dry food within a certain time after opening (check the bag for its guidance), so a big bag for a small dog is a false economy.
Matching bag size to freshness
If the maker advises finishing a bag within about six weeks of opening, the right bag size is the daily grams times 42. A simple version of this rule is below.
| Dog | Daily grams | Largest bag to finish in 6 weeks (42 days) |
|---|---|---|
| 5 kg | 104 | 4.4 kg |
| 10 kg | 175 | 7.4 kg |
| 20 kg | 294 | 12.3 kg |
| 30 kg | 399 | 16.8 kg |
Use the freshness time on your own bag, not six weeks. Buying the next size down from the largest in the table avoids waste. If the larger bag is cheaper per kilogram, compare the saving with the risk of stale food and waste; a bag that is partly thrown away is not a bargain. The cost lines are in our guide to how much dog food costs per month.
Storage that protects the food
Dry food loses quality when exposed to air, heat, light and moisture. Good practice, which you should check against your maker’s advice, includes:
- Keep the food in its original bag, which has a barrier layer, and put the bag inside a sealed container.
- Store in a cool, dry place, not in a hot garage or a damp shed.
- Wash and dry the container between bags, so old crumbs do not contaminate new food.
- Keep the batch code and best-before date by writing them on the container or taking a photo.
- Use a clean scoop and keep it out of the bag.
- Do not top up old food with new; finish one bag before starting the next.
If the food smells off or looks mouldy, do not feed it, and contact the maker.
Wet food and mixed feeding
For cans and trays, the same idea applies, with cans instead of kilograms. If a dog needs 3.2 cans of 330 kcal a day, a case of 12 lasts 3.75 days. When you feed a mix, work out the days for each part separately: a dry bag lasts longer if part of the calories come from wet food. The Dog Wet & Dry Food Calculator gives the split and our guide to feeding wet and dry together shows the arithmetic.
Setting a reorder reminder
The Pet Food Run-Out Date Calculator takes the amount left and the daily grams and gives a date. A practical routine:
- Weigh the remaining food, or estimate it from the bag.
- Divide by the daily grams to get days left.
- Count forward to find the run-out date.
- Subtract the delivery time plus a week of buffer to get the reorder date.
- Put it in your calendar.
For example, 3,000 g left at 294 g a day is 10.2 days. If delivery takes four days and you want three spare days, order within three days.
When the numbers change
Recalculate when the dog’s weight changes, when you start or stop a diet, when you change food, when the dog moves to a new life stage and when treats change. A puppy’s daily grams change every week or two, so a bag may last a different time from the first calculation. A dog on a weight-loss plan eats less, so a bag lasts longer. Update your reminder each time.
Several dogs and shared bags
With two dogs, add their daily grams. A 20 kg dog (294 g) and a 10 kg dog (175 g) eat 469 g a day together, so a 15 kg bag lasts 32 days. Keep a note of each dog’s amount so that no one is overfed, and feed separately if one steals. If the dogs eat different foods, work out each bag separately.
Common mistakes
- Using the bag’s cups or table instead of calculated grams.
- Buying a bag too large for a small dog.
- Forgetting treats.
- Not updating when weight changes.
- Leaving the bag open.
- Mixing old and new food.
- Waiting until the bowl is empty to reorder.
Worked examples for four households
Four households, four sets of numbers. All dogs are neutered adults on a 3,600 kcal/kg food.
| Household | Dogs | Daily grams | Bag | Days | Reorder by |
|---|---|---|---|---|---|
| Flat, one small dog | 5 kg | 104 | 5 kg | 48 | Day 41 |
| Family, one medium dog | 20 kg | 294 | 10 kg | 34 | Day 27 |
| Two dogs | 20 kg + 10 kg | 469 | 15 kg | 32 | Day 25 |
| Large dog | 30 kg | 399 | 15 kg | 38 | Day 31 |
The reorder day assumes a week of buffer. For the two-dog household the 15 kg bag lasts 32 days, which is a sensible fit with a six-week freshness period. For the flat with a small dog, a 5 kg bag at 48 days is about right; a 10 kg bag at 96 days would be too much.
What to do with leftovers when you switch food
If you change food, you may have a part-used bag. Use it up in the transition. For a seven-day switch, the old food needed is about half a day’s ration for each of the first four days and less after, as in how to switch dog food. A dog eating 294 g needs about 1,000 g of the old food over the week. Anything left can be used as training kibble, if fresh, or discarded if past its date. Do not donate opened food unless it is clearly fresh and the recipient accepts it.
Estimating without weighing
Sometimes you cannot weigh the food left. Use the bag’s markings, a measuring cup or the depth in a container. If a container holds 10 kg when full and is now a third full, about 3.3 kg remains. Divide by daily grams to find days: 3,300 ÷ 294 = 11 days. Check the estimate by weighing when you can, and note the date of your last measurement. Over time you will learn how fast your dog goes through food.
Questions owners ask in more depth
My bag lasts a week longer than the calculation. Why? Common reasons are treats that replace some meals, a dog that sometimes leaves food, a scoop that is slightly under-filled or a daily amount that is a little below what you calculated. If your dog is a healthy weight, it does not matter; if it is losing weight, check the amounts.
My bag runs out a week early. Why? Heaped scoops, spills, extra feeding by other people or food given to another pet are the usual causes. Weigh a week of food into a container to see where it goes.
Is it worth buying a bigger bag during a sale? Only if you will use it while fresh and the price per kg is lower after allowing for waste. For a 5 kg dog, a 15 kg bag takes 144 days; unless you can divide and freeze it as the maker allows, the saving is unlikely.
Can I split a bag with a friend? Yes, if both dogs eat the same food and the bag is divided into clean, sealed containers soon after opening. Label the batch code.
Should I keep the original bag? Yes, inside a container, because the bag has the batch number, best-before date and feeding information, which matter if there is a recall.
How do I know when food has gone off? A rancid smell, a change in colour, mould or insects mean it should not be fed. Throw it away safely and, if the date has not passed, tell the maker.
Subscriptions, deliveries and stock-outs
Delivery services make reordering easy, but they can lock you into a schedule that no longer fits. If a subscription sends a 10 kg bag every 30 days and your dog eats 294 g a day, it is using 8.8 kg, so you build up stock at the rate of 1.2 kg a month, and after a year you hold 14 kg of surplus. Set the interval from the sum, not from the default, and review it each time your dog’s weight or food changes. Keep one spare bag if a stock-out would be a problem, but rotate it so the oldest is used first, and check the dates.
| Interval | Food sent per month (10 kg bag) | Dog’s use per month (294 g/day) | Surplus per month |
|---|---|---|---|
| Every 30 days | 10.0 kg | 8.8 kg | 1.2 kg |
| Every 34 days | 8.8 kg | 8.8 kg | 0 |
| Every 40 days | 7.5 kg | 8.8 kg | −1.3 kg (run short) |
Quick summary
- Days a bag lasts = bag grams ÷ daily grams.
- A neutered 20 kg dog on 294 g a day finishes a 10 kg bag in 34 days and a 15 kg bag in 51.
- Choose a bag size you can finish within the maker’s freshness period.
- Store food in its bag inside a sealed container, cool and dry.
- Set a reorder date a week before you run out.
- Use the Pet Food Bag Duration Calculator.
Frequently asked questions
How do I work out how long a bag of dog food will last?
Divide the bag weight in grams by the dog's daily grams. A 10,000 g bag at 294 g a day lasts about 34 days.
How long does a 15 kg bag last for a 10 kg dog?
A neutered 10 kg dog eats about 175 g a day, so a 15 kg bag lasts about 86 days, longer than many makers advise for freshness.
Should I buy the biggest bag?
Only if you can use it within the freshness period and the price per kg is lower. Otherwise a smaller bag is better.
How should I store dry dog food?
In its original bag inside a sealed container in a cool, dry place, following the maker's advice.
How do I know when to reorder?
Work out the run-out date and reorder when about a week remains to allow for delivery.
What if my dog's weight changes?
Recalculate the daily grams and the run-out date.
Do treats change the answer?
Yes: treats come out of the meals, so the bag lasts a little longer if treats are not from the same food.
Sources
- NRC (2006) Nutrient Requirements of Dogs and Cats, National Academies Press
- Pure arithmetic: days = bag grams ÷ daily grams
Related calculators
- Pet Food Bag Duration CalculatorFind out how many days a bag of pet food will last at the amount you feed.
- Pet Food Run-Out Date CalculatorFind the date a bag of food will run out and when to reorder.
- Dog Food CalculatorTurn your dog's daily calorie need into grams and cups of the food you actually feed, using the energy value printed on the bag.
Keep reading
- How Much Should I Feed My Dog? By WeightHow much to feed a dog by weight: a grams and cups chart, how to read the food label, meals per day, adjusting by body condition and common mistakes.
- Dog Feeding Chart by Weight (Printable)A printable dog feeding chart by weight: daily calories for neutered, intact and inactive adults, with grams for 3,400, 3,600 and 3,800 kcal/kg foods.
- How Many Cups of Dry Food Should a Dog Eat?How many cups of dry food a dog needs: the calorie method, a cups chart for 300, 360 and 400 kcal per cup, why cups vary and how to measure accurately.
- Pet Sitter vs Boarding: Cost ComparisonHow to compare boarding, drop-in visits and an overnight sitter: rate × nights, a 3 to 14 night table, extras, break-even rates and what price cannot tell you.