How long does a bag of dog food last? Days by bag size

By Alex Baer · Updated July 2026

Bag sizes are printed in pounds, but dogs eat in calories. The same 30 lb bag can feed one dog for three months and be gone in a month with another. The good news: the math is simple, and you only need two numbers, how many calories your dog needs per day and how many calories the bag holds.

This guide walks through the calculation, gives you a quick days-per-bag calculator, and includes a reference table for common bag sizes. Calorie numbers come from the 180 dry foods in our database, and the formulas are the same ones behind our portion calculator.

41 days
how long a 30 lb bag of a typical dry food lasts a 60 lb dog

Rule of thumb. One pound of dry dog food holds about 4 cups. Days per bag = bag weight in pounds times 4, divided by the cups your dog eats per day.

The math, step by step

Step 1: count the cups in the bag. The median cup of dry dog food weighs 112 grams across the dry foods in our database, which works out to about 4 cups per pound. So a 15 lb bag holds roughly 61 cups, a 30 lb bag about 121 cups, and a 50 lb bag about 202 cups.

Step 2: your dog's cups per day. Daily calories come first: an adult neutered dog with moderate activity needs about 70 × (weight in kg)^0.75 × 1.4 kcal per day, the same RER and MER math our calculator uses. Divide that by your food's calories per cup. The median in our database is 397 kcal per cup, and the exact number is printed on the bag label.

Step 3: divide. Cups in the bag ÷ cups per day = days the bag lasts.

Worked example: 60 lb Labrador, 30 lb bag. RER = 70 × (27.2 kg)^0.75 ≈ 834 kcal. Neutered adult, moderate activity: 834 × 1.4 ≈ 1,168 kcal a day. At 397 kcal per cup that is 2.9 cups a day. The bag holds about 121 cups, so 121 ÷ 2.9 ≈ 41 days. Call it six weeks.

Days per bag: quick check

Defaults are database medians for dry food (397 kcal and 112 g per cup). Your formula will differ, check the bag label.

For a result personalized to your dog's breed, age, and activity, use the full calculator.

Estimates only, not veterinary advice. Assumes a neutered adult dog.

Days per bag by dog weight (typical dry food)
Dog weight	Cups per day	15 lb bag	30 lb bag	50 lb bag
10 lb	0.8	79 days	158 days	264 days
20 lb	1.3	47 days	94 days	157 days
35 lb	2.0	31 days	62 days	103 days
50 lb	2.6	23 days	47 days	79 days
65 lb	3.1	19 days	38 days	64 days
90 lb	4.0	15 days	30 days	50 days

Assumes a neutered adult dog with moderate activity, 397 kcal and 112 g per cup (median values across the dry foods in our database). Days rounded down.

Watch out. Calories per cup range from 243 to 528 across the dry foods in our database. The same bag size can last a third longer or run out weeks sooner depending on the formula. Check the kcal per cup line on your own bag before trusting any average, including ours.

Do not buy more than six weeks of food

Bigger bags are cheaper per pound, but an opened bag of kibble is best used within about six weeks: the fats slowly oxidize and the food goes stale once air gets in. If the table above says a bag would last your dog three months, size down. The sweet spot is a bag your dog finishes in four to six weeks after opening.

Frequently asked questions

How long does a 30 lb bag of dog food last a 60 lb dog?

About 41 days at a typical 397 kcal per cup: a 60 lb neutered dog with moderate activity needs roughly 1,170 kcal a day, which is 2.9 cups, and a 30 lb bag holds about 121 cups. A denser or lighter formula shifts that by a week or more in either direction.

How many cups of dog food are in a bag?

Roughly 4 cups per pound. The median cup of dry food in our database weighs 112 grams, so a 15 lb bag holds about 61 cups, a 30 lb bag about 121 cups, and a 50 lb bag about 202 cups. Cup weight varies from 82 to 130 grams by formula, so treat these as close estimates rather than exact counts.

Is it cheaper to buy the biggest bag?

Per pound, usually yes, and our cost comparisons use the largest available bag for exactly that reason. But if your dog will not finish the bag within about six weeks of opening, the food may go stale before the savings pay off. Match the bag to your dog's pace using the table above.

The short version

One pound of dry food is about 4 cups (median 112 g per cup in our database).
Days per bag = cups in the bag divided by your dog's cups per day.
A 30 lb bag lasts a 60 lb dog about six weeks, and a 20 lb dog about three months.
Calories per cup vary from 243 to 528 by formula, so check your own bag's label.
Pick a bag your dog finishes within four to six weeks of opening.

More guides: How much should I feed my dog? · Fresh vs kibble: what dog food actually costs · How to switch dog food safely

PetPortions provides portion and cost estimates, not veterinary advice. Estimates are based on breed averages. Consult your vet for medical conditions or unusual diets.