Giant dogs eat far more than most owners expect, and the bag label rarely helps. A Great Dane, a Mastiff or a Saint Bernard can need twice the food of a medium dog, and a small error in the daily portion adds up to kilos of extra weight over a year. This free calculator gives you a clear daily amount in grams, so you can feed with confidence instead of guessing from a scoop.
Start with your dog's weight in kilos. If you do not know the exact weight, weigh yourself holding the dog and then weigh yourself alone, and subtract the second number from the first. For a giant dog, a vet scale is best, because even two or three kilos change the result. Enter the weight honestly, not the target weight, unless your vet has told you to feed for a lower weight.
Next, find the energy value on the food bag. It is usually printed as kilocalories per kilo, for example 3,800 kcal per kg. Different foods vary a lot, and a rich food needs fewer grams than a light food, even though the dog eats the same amount of energy. That is why grams alone mean nothing without the energy value, and why switching brands means recalculating the portion.
Then choose the activity level. A calm giant dog that sleeps most of the day needs less than a dog that runs, swims or works. Growing giant puppies need the most energy for their size, because they are building bone and muscle at a fast rate. If you are unsure, pick the moderate level and adjust after two weeks based on body condition.
The calculator first estimates resting energy from body weight, then multiplies it by an activity factor. The result is a daily energy need in kilocalories, converted into grams of your chosen food. It also splits the day into two meals, which suits most giant breeds, and shows the monthly use in kilos so you can plan shopping and storage.
Use the grams result with a kitchen scale, not a cup, for at least the first two weeks. Cups vary by food shape and by how full you fill them, and a 10 percent error on 600 grams is 60 grams a day. Weighing takes ten seconds and removes the biggest source of feeding mistakes. After that, you can mark the right level on your scoop if you prefer cups.
Watch your dog's body, not just the number. You should be able to feel the ribs with light pressure but not see them clearly, and the waist should narrow slightly behind the ribs when viewed from above. If the ribs disappear under a thick fat layer, cut the portion by 10 percent and recheck in two weeks. If the ribs and hip bones stand out, add 10 percent and recheck the same way.
Giant breeds grow slowly and mature late, often not before 18 to 24 months. During growth, too much food can speed up growth and stress young joints, while too little food slows development. That is why giant puppies need regular weigh-ins, about once a month, and a portion that changes as they grow. Bring the calculator result to vet visits and ask whether it matches the growth curve.
Treats count as food. Training treats, dental chews and table scraps all add energy, and for a giant dog they can easily reach 10 percent of the daily total. If you give many treats on training days, reduce the main meals a little on those days. Keep treats small and low in fat, and avoid cooked bones, which can splinter and cause serious harm.
Feeding times matter too. Split the daily amount into at least two meals, morning and evening, and avoid heavy exercise right before or after eating. Giant breeds face a higher risk of bloat, a dangerous stomach condition, so calm feeding, a steady routine and no gulping help. If your dog eats very fast, a slow feeder bowl is a cheap and useful change.
Finally, remember that this tool gives a guide, not a medical plan. Dogs with kidney disease, diabetes, allergies or weight problems need a vet or a veterinary nutritionist to set the diet. If your dog loses or gains weight fast, vomits often, has ongoing diarrhoea or refuses food for more than a day, contact your vet promptly instead of adjusting the portion yourself.