It is one of the questions we get asked most often, and it is a good question to ask, because the feeding guide printed on a bag of food is only ever a starting point. It is worked out for an 'average' dog of a given weight, and your dog is not average — they have their own metabolism, activity level, and body shape. The good news is that you do not need to guess. Working from your dog's energy needs in calories, rather than cups or scoops, gives you a far more reliable starting point, and our dog food calculator at /dog-food-calculator will do the maths for you in seconds.
The scientific starting point is something vets call resting energy requirement, or RER. The formula is 70 multiplied by your dog's body weight in kilograms, raised to the power of 0.75. This sounds fiddly, but it simply reflects the fact that energy needs do not scale in a straight line with weight — a 40kg dog does not need four times as much as a 10kg dog, because bigger animals are proportionally more efficient. RER represents the calories your dog would burn lying quietly all day: breathing, keeping warm, digesting, and running all the background processes of life.
From resting energy to daily calories
Real dogs do rather more than lie still all day, so RER is then multiplied by a life-stage and activity factor to get daily energy requirement (DER). Typical multipliers used by vets are around 1.2 to 1.4 for a neutered, sedentary adult; 1.4 to 1.6 for an intact adult or a moderately active neutered dog; and up to 2 or more for working dogs, or dogs who are still growing. Puppies have particularly high demands relative to their size because they are building bone, muscle and organs from scratch — a young puppy can need two to three times the resting energy requirement of an adult of the same weight.
Senior dogs, by contrast, often need less energy than they did in middle age, partly because muscle mass naturally declines and partly because many older dogs are simply less active. This is one of the most common reasons dogs put on weight in their later years despite eating 'the same as always' — their needs have quietly reduced even though the bowl has not.
Feed for the weight you want, not the weight you have
If your dog is at a healthy weight already, use their current weight in the calculation. But if your dog needs to lose weight, this is the single most important tweak: calculate calories for their ideal weight, not the weight they are carrying now. Feeding for a heavier body simply maintains that heavier body. Our body condition score guide at /dog-body-condition-score will help you and your vet agree what that ideal weight realistically looks like, since breed standard weight ranges can be surprisingly wide.
For weight loss, most vets recommend aiming for roughly one to two per cent of body weight lost per week — slow and steady is safer for joints and metabolism than a crash diet, and it is far more likely to stay off. Weight loss plans should always be done with your vet's knowledge, particularly for dogs with any underlying health conditions.
Weighing food properly makes a bigger difference than you'd think
A kitchen measuring scoop is a surprisingly unreliable tool. Studies have shown that the same scoop, used by different people, can deliver portions that vary by as much as 100 grams either way — for a small dog, that is potentially half their daily allowance. Digital kitchen scales cost very little and remove this guesswork entirely. Weigh the daily total, then split it across two to four meals depending on your dog's age and preference; puppies generally do best with more frequent, smaller meals.
- Weigh dry food in grams rather than using a scoop or cup.
- Split the daily total across two to four meals rather than one large one.
- Recalculate roughly every two to four weeks, or after any noticeable weight change.
- Adjust portions up or down by about ten per cent at a time and reassess.
Treats count too
Treats, training rewards, chews and anything shared from the table should together make up no more than around ten per cent of your dog's daily calories. It is easy to underestimate this — a single dental chew or pig's ear can run to well over 100 kcal, which is a substantial chunk of a small dog's whole daily budget. Our treat translator at /treat-translator converts common treats into their human food equivalent, which is often a genuinely eye-opening exercise for owners.
Rather than treating on top of meals, it is better to deduct the treat calories from that day's food allowance, or to use part of the dog's normal kibble ration as training rewards throughout the day.
What the numbers mean
When our dog food calculator gives you a daily calorie figure and a gram amount, treat it as a well-informed starting point rather than a rule carved in stone. Two dogs of identical weight, breed and age can have genuinely different metabolisms. The numbers get you close; your dog's body condition, energy levels and coat quality over the following weeks tell you whether you have got it right.
Signs you may need to adjust
Keep half an eye on your dog between formal weigh-ins. You should be able to feel — though not necessarily see — their ribs with light pressure, and there should be a visible waist when viewed from above and a natural tuck up behind the ribs from the side. If ribs become hard to feel, or your dog seems constantly hungry and is losing condition, it is worth reassessing sooner rather than waiting for the next scheduled check.
When to speak to your vet
Do speak to your vet before making significant changes to feeding for a puppy, a dog with a medical condition, a pregnant or nursing dog, or any dog who is significantly over or under their ideal weight. They can also advise on the right food type and any supplements needed. Remember that any calculator, including ours, gives you a guide — your vet's hands-on assessment of your individual dog always takes priority.