It is one of the most searched questions about dogs and it has no single answer, which is why the search results are so unsatisfying.
What it does have is a reliable method, and the method is not arithmetic on the back of a bag. It is a starting estimate followed by measurement against the dog in front of you.
Why the bag cannot answer this
The feeding guideline on a bag of food is produced for an enormous population of dogs. It covers a weight band, and every dog in that band gets the same number.
Within that band you have a neutered eight-year-old Labrador who walks twenty minutes a day and an intact three-year-old working dog of the same weight. Their energy requirements are not similar.
Published estimates of individual maintenance energy requirements in dogs typically vary by a factor of roughly one and a half to two around the average for the same body weight. So a number that is correct on average can be substantially wrong for your particular dog and still be a perfectly reasonable guideline.
Guidelines are a place to begin. The dog is the measurement.
There is also a commercial point worth naming honestly. Manufacturers have no incentive to understate portions, and guidelines across brands do tend to sit toward the generous end. That does not make them dishonest. It does mean starting at or slightly below the guideline for an average pet dog is usually sensible.
What actually determines how much a dog needs
Weight, which is the input the bag uses, and the biggest single factor.
Neuter status. Neutered dogs generally have lower energy requirements than intact dogs, commonly cited as roughly twenty to thirty percent lower. This is one of the most common causes of unintended weight gain, because the food does not change when the dog does.
Age. Puppies need considerably more energy per kilogram than adults. Older dogs often need less, though not always, and some seniors need more as they lose condition.
Activity. Not walk length but total energy output. A dog who spends two hours running is in a different category from a dog who walks calmly for two hours.
Breed and individual metabolism. Some breeds are notably prone to weight gain, and individual variation within a breed is large.
Health conditions. Several, including thyroid problems, affect weight and appetite. This is part of why unexplained weight change belongs with a vet rather than with a measuring scoop.
Environment. Dogs kept outdoors in cold conditions have higher requirements than indoor dogs.
Body condition scoring, which you do with your hands
This is the skill worth actually learning, and it takes about a minute.
Body condition scoring is a standard veterinary assessment, usually on a nine-point scale where four to five is ideal. It has three parts.
Ribs. Run your hands flat along the dog's side with light pressure. You should be able to feel the ribs easily, with a thin layer of fat over them. Think of the back of your hand with fingers spread: that is roughly what ideal feels like. If you have to press to find ribs, the dog is carrying too much. If ribs are prominent and sharp with no covering, too little.
Waist from above. Stand over the dog looking down. There should be a visible narrowing behind the ribs. Straight sides or an outward bulge means overweight.
Tuck from the side. Viewed from the side, the abdomen should rise upward from the ribcage toward the hind legs rather than running parallel to the ground.
Coat length hides all of this visually, which is exactly why it is a hands-on assessment rather than a look.
Breed caveat. Body shape varies. Sighthounds are naturally leaner and visible ribs can be normal for them. Some breeds have conformation that makes the standard assessment harder to read. If you are unsure what ideal looks like for your dog, ask your vet to score the dog with you once. It takes two minutes and it recalibrates your eye permanently.
The reason this matters more than any calculation: studies of dog owners consistently find that a substantial proportion of owners of overweight dogs assess their dog as normal weight. The eye adjusts to what it sees regularly, and most of us see mostly overweight dogs.
Using the bag properly as a starting point
The method in five steps.
One. Weigh the dog. Most veterinary practices have scales in reception and will let you use them without an appointment. Small dogs can be weighed by standing on bathroom scales holding the dog and subtracting.
Two. Read the guideline for that weight, noting that some bags give the guideline for target weight rather than current weight. If your dog needs to lose, feed for the target rather than the current figure, and get the target from your vet.
Three. Adjust for the obvious factors. Neutered and low activity, start at the lower end or slightly below. Intact, young and genuinely active, start at the upper end.
Four. Weigh the food. This is the single highest-value change most households can make. Kitchen scales, in grams. Studies comparing measuring cups to weighed portions have found errors in both directions of a magnitude that easily accounts for slow weight gain, and scoops vary enormously in how tightly people fill them.
Five. Split it into meals. Twice daily suits most adult dogs. Puppies need more frequent meals. Deep-chested breeds are often fed smaller meals more often and asked to avoid vigorous exercise immediately around eating, on the grounds of bloat risk; your vet is the right source on that for your specific dog.
How this is taught inside Astra Trainer
Portion sizing sits in the Nutrition & food direction of the Dogs world, which covers reading labels, portioning, weight and body condition, sensitive stomachs, digestive clues, allergies and picky eaters across seven courses.
The direction is framed around cutting through marketing to work out what a specific dog needs, rather than recommending a brand. Lessons run about five minutes, and there is a guide inside for anything that does not look right.
The treat arithmetic almost everyone gets wrong
The standard guidance is that treats should make up no more than about ten percent of daily calories.
Work it through for a ten kilogram dog. That dog might need somewhere in the region of 400 to 550 calories a day depending on everything above. Ten percent is roughly 40 to 55 calories.
Forty calories is a very small amount of food. A single moderately sized commercial dog biscuit can approach it. A dental chew often exceeds it. A slice of cheese roughly doubles it.
Now add a household of three people who each give the dog something during the day, plus training treats, plus what falls off the table.
This is the mechanism behind most slow weight gain, and it is invisible because no individual item looks significant. The food bowl portion is carefully weighed and the other thirty percent of intake goes unrecorded.
Three practical fixes.
Measure the day's treat allowance into a container in the morning. When it is empty, that is the day. This also solves the multiple-people problem without anyone having to keep count.
Use part of the meal ration for training. Take the day's kibble, set some aside, train with it. Extremely effective and it costs nothing calorically.
Use lower-calorie options for high-volume training. Small pieces of appropriate vegetables work well for many dogs. Check which are safe first, because several common human foods are toxic to dogs, including grapes, raisins, onions, garlic, chocolate and xylitol.
How to adjust, and how slowly
Set the starting portion, then check body condition every two weeks and weigh monthly.
If the dog is gaining unintentionally, reduce by around ten percent and reassess in two to four weeks. Do this before assuming the food is wrong.
If the dog is losing unintentionally, that is a different situation. Unexplained weight loss is a veterinary matter first, not a portion adjustment. Rule out a medical cause before simply feeding more.
If deliberate weight loss is the goal, that belongs with your vet. Safe rates of weight loss in dogs are slower than most owners expect, commonly cited around one to two percent of body weight per week, and severe restriction risks nutritional deficiency because cutting the food cuts the vitamins and minerals with it. Vets use prescription weight-management diets partly for this reason: they reduce calories while holding nutrient density.
Adjust one thing at a time and give it a few weeks. Changing food and portion and treat policy simultaneously means you will not know what worked.
Puppies, seniors and the special cases
Puppies. Higher energy requirements per kilogram, and they change quickly, so portions need revisiting frequently. Large and giant breed puppies are a genuine special case: overfeeding and excessively rapid growth are associated with developmental orthopaedic problems, and these puppies need a food formulated for large breed growth with controlled calcium. Your vet is the right source here, and this is one of the few areas where getting it wrong has lasting consequences.
Seniors. Often less active and needing fewer calories, but not universally. Some older dogs lose muscle and condition and need more. Body condition remains the measure. Weight change in an older dog is also worth a vet conversation, because it is a common early sign of several conditions.
Pregnancy and nursing. Requirements rise substantially, particularly during lactation. Veterinary guidance, not guesswork.
Working dogs and high-performance dogs. Requirements can be several times maintenance.
Why the observation habit is the actual skill
Everything above reduces to one practice: assess the dog regularly and adjust slowly. That is a habit, and habits are what get dropped.
Astra Trainer is built around that problem. Daily quests, points and a streak keep short lessons running, with a streak shield for the day life gets in the way. Quizzes follow each topic and each course closes with a ten-question final exam, so what you learn gets checked rather than skimmed. The daily Connections round and the 10x10 crossword are generated from this world's own lessons, and a Circle gives you a small group with a shared weekly goal.
Seven worlds are included in one pass. The Dogs world alone runs to four directions and thirty courses.
The dog who is always hungry
Worth addressing because it drives a lot of overfeeding.
Many dogs behave as though they are starving regardless of what they have eaten. Food-seeking behaviour is not a reliable indicator of caloric need, and in several breeds it is close to a defining trait. Labradors have been the subject of research on a genetic variant associated with food motivation.
So the dog's opinion is not evidence. Body condition is.
That said, a genuine and sudden change in appetite is different from a dog who has always been food-obsessed. A dog whose hunger noticeably increases, or who starts losing weight while eating well, should see a vet, because several conditions present that way.
For the ordinary always-hungry dog, practical measures help: feeding the same amount across more meals, slow feeders and puzzle feeders that extend eating time, and foods with higher fibre content that increase satiety, which is one of the design principles behind veterinary weight-management diets.
What to take from this
The bag gives you a starting point across a very wide population. Your dog is one individual within it.
Learn body condition scoring, do it by hand every couple of weeks, and ask your vet to score your dog with you once so your eye is calibrated.
Weigh the food in grams. The cup is costing you accuracy you did not know you were losing.
Count the treats, because they are almost certainly more than you think, and put the day's allowance in a container if more than one person feeds the dog.
Adjust by about ten percent at a time and wait several weeks. And take unexplained weight change, in either direction, to a vet rather than to a measuring scoop.
How do I know if my dog is overweight?
Assess by hand rather than by eye. You should feel ribs easily under a thin fat layer, see a waist from above, and see an upward tuck from the side. If you have to press to find ribs, the dog is carrying too much. Ask your vet to score your dog with you once to calibrate.
Should I feed once or twice a day?
Twice daily suits most adult dogs. Puppies need more frequent meals. Deep-chested breeds are often fed smaller, more frequent meals on bloat-risk grounds, and that is a question for your vet about your specific dog.
Do I really need to weigh the food?
It is the single highest-value accuracy improvement available. Volume measurement with a cup or scoop is inconsistent enough to account for slow, unexplained weight gain on its own.
My dog acts starving all the time. Is he underfed?
Food-seeking behaviour is not a reliable indicator of need, and in some breeds it is close to a defining trait. Body condition is the measure. A sudden change in appetite, though, is worth a veterinary conversation.
Where can I learn this properly?
The Nutrition & food direction inside the Dogs world of Astra Trainer covers portioning, body condition, labels, digestive clues and allergies across seven courses of about five-minute lessons. You can see what is inside here.