How much should I feed my dog or cat? Calories first, then grams

Work out how many calories your pet needs in a day, then divide by the calories in its food to get grams. For an adult pet you start with resting energy, which is 70 × (weight in kg)^0.75, and multiply it by a factor for neuter status and activity. After that you weigh your pet every week or two and adjust. Every step is below, worked through with example numbers.

I make Dog & Cat Nutrition Coach. The app and the two free calculators on this site use the same maths as this page. The number you end up with is an estimate to start from. It isn’t a prescription, and your vet knows your pet, so if they give you a different number, go with theirs.

Step 1: Weigh your pet

You need a scale that shows small changes. With a cat or a small dog, the easy way is to weigh yourself holding the pet and subtract your own weight. A baby scale or a kitchen scale works too. Write the weight down in kilograms. If your scale shows pounds, divide by 2.2046. A 10 lb cat is 4.54 kg, and a 50 lb dog is 22.7 kg.

While you’re at it, give your pet a body condition score (BCS). Vets use a scale from 1 to 9, and 5 is ideal. A dog at 5 has ribs you can feel without pressing hard, and an obvious waist when you look down from above. A cat at 5 has ribs you can feel with light pressure and a visible waist from above. If you’re not sure, ask your vet to score it at the next visit. For weight loss, it’s the number that matters most.

Step 2: Resting energy requirement (RER)

Resting energy requirement is the energy a pet uses just staying alive. The AAHA and WSAVA nutrition guidance start every daily-calorie estimate from it.

RER (kcal per day) = 70 × (body weight in kg)^0.75

On a phone calculator in scientific mode, type the weight in kg, raise it to the power 0.75 with the x^y key, and multiply by 70. A basic calculator can do it too if you take the square root twice and then cube the result. For 5 kg, two square roots give 1.495, cubed that’s 3.34, and times 70 it’s 234. Or skip the arithmetic and read it off the table.

Step 3: Multiply for activity and neuter status

A pet going about a normal day burns more than its resting energy. How much more depends on whether it’s a dog or a cat, whether it’s spayed or neutered, and how active it is. Dogs sit higher on the scale than cats. The multipliers below are the ones the app and the calculators use. I picked them from the ranges in AAHA/WSAVA-style guidance. Different vets use slightly different figures, so think of these as a middle-of-the-road start.

Two worked examples. Take a neutered 20 kg dog that gets regular walks. Its RER is 662, and 662 × 1.6 is about 1,059 kcal a day. Now a neutered 4 kg indoor cat with regular play. Its RER is 198, and 198 × 1.2 is about 238 kcal a day. That cat number is small, and it doesn’t take many extras to go over it.

This page doesn’t cover puppies and kittens, pregnant or nursing pets, seniors with health conditions, or any pet with diabetes, kidney, heart or other disease. Their needs are different, and their vet should set the number.

Step 4: Turn calories into grams

Find the calories on the food label and look for “kcal per 100 g”. If yours says “ME kcal/kg” instead, divide that by 10 and you have kcal per 100 g. Then work out the grams.

grams per day = daily kcal ÷ (kcal per 100 g) × 100

• The 20 kg dog from step 3, on a kibble with 380 kcal per 100 g: 1,059 ÷ 380 × 100 is about 279 g a day.
• The 4 kg cat on a dry food with 380 kcal per 100 g: 238 ÷ 380 × 100 is about 63 g a day. On a wet food with 90 kcal per 100 g, the same 238 kcal comes to about 264 g a day.
• Feeding half dry and half wet? Split the calories first and convert each half. 119 kcal of the dry food is about 31 g, and 119 kcal of the wet food is about 132 g.

Weigh the food on a kitchen scale rather than using a scoop. A “cup” of kibble can be off by tens of percent depending on the kibble and how tightly it’s packed, and all of that difference is calories. What matters is the daily total. How you split it across meals is a routine question for your vet.

Step 5: Count the treats

Treats count toward the day. A common rule of thumb among vets is to keep treats under 10% of daily calories. The app uses 10% when a pet is at maintenance and tightens it to 8% during weight loss. For the 20 kg dog, 10% of 1,059 is about 106 kcal of treats. For the 4 kg cat it’s about 24 kcal. Whatever you give as treats, take it off the meals so the day still adds up.

Step 6: Let the scale correct the number

Every formula describes an average pet, and yours isn’t one. So treat the number as a first guess and let the scale tell you how close it was.

1. Feed the calculated amount for two weeks. Weigh it out, and count the treats.
2. Weigh your pet every one to two weeks, on the same scale and at the same time of day.
3. If the weight is holding steady and that’s what you want, carry on. If it’s drifting the wrong way, change the daily amount by a small step. The app moves the target about 5% at a time and then waits for the next weigh-ins. For a pet at maintenance, it counts a week-to-week change of up to about 0.5% of body weight as stable.
4. Score body condition again every month or two. The weight can stay the same while muscle replaces fat, or the other way round.

If your pet needs to lose weight

Please do this with your vet. They can confirm your pet really is overweight and rule out a medical reason, and the two of you can agree on a goal weight. After that, the maths is different for dogs and cats, and the difference matters.

Dogs: scaled to activity, on current weight

For a dog, the starting target is RER at its current weight times a weight-loss factor. That factor is 0.80 for a mostly resting dog, 0.85 for one that gets regular walks, 0.90 for free outdoor access or a very playful dog, and 1.00 for a dog that’s constantly active. If the dog isn’t neutered, multiply by 1.05 as well. The target never goes below 0.60 × RER at the current weight. Take a neutered 6 kg dog at BCS 7 that gets regular walks. Its RER is 268, and 268 × 0.85 gives about 228 kcal a day. For comparison, its maintenance number would be about 429.

Cats: fixed rate, on ideal weight

For a cat, the target is 0.80 × the RER at the cat’s ideal weight. That rate is fixed. It doesn’t change with activity, and it never goes lower. Ideal weight is estimated from the BCS. For a cat, divide the current weight by (1 + 0.10 × (BCS − 5)). For a dog, divide by (1 + 0.13 × (BCS − 5)). Say you have a 6 kg cat at BCS 7. Its estimated ideal weight is 6 ÷ 1.2 = 5 kg. RER at 5 kg is 234, and 234 × 0.80 is about 187 kcal a day. The same cat’s maintenance number would be about 322.

I kept the cat numbers cautious on purpose. If a cat eats too little for too long, its body releases fat faster than the liver can process it. Within days that can become a life-threatening liver condition called hepatic lipidosis. So weight loss for a cat goes slowly, with frequent weigh-ins. Please don’t just halve the bowl.

Signs to stop and call the vet

• A cat that keeps refusing meals. In the app, three refused meals in three days, or two days in a row of eating less than half the target, stops the target from going any lower and tells you to contact a vet.
• Weight dropping faster than about 1.5% of body weight a week. The app flags that as too fast.
• Any pet that’s losing weight when you didn’t mean it to.

Common questions

How many calories a day does a 10 lb cat need?

A 10 lb cat is 4.54 kg, which gives a resting energy of about 218 kcal. If it’s neutered, lives indoors and gets regular play (factor 1.2), that’s about 261 kcal a day. A lazier indoor cat (1.0) needs about 218. An active outdoor cat can need 300 or more. Start there, then weigh and adjust.

How many calories a day does a 50 lb dog need?

A 50 lb dog is 22.7 kg, which gives a resting energy of about 728 kcal. A neutered dog with regular walks (factor 1.6) needs about 1,165 kcal a day. An intact dog that’s very active (2.2) needs about 1,600.

How many cups is that?

That depends on the food. If the label gives kcal per cup, divide your daily kcal by it. Many give kcal per kg instead, and then it’s easier to use the gram method from step 4 and weigh the food.

Why is the bag’s feeding chart different from my number?

The chart on the bag gives a range for a typical pet of that weight. Neuter status, activity and body condition can push your pet’s real need up or down, which is why steps 3 and 6 are there. If the two numbers are far apart, ask your vet.

Is a dog’s formula the same as a cat’s?

The resting-energy formula is the same for both. The multipliers are different, and so is weight loss. For a dog, the target is based on current weight and scaled by activity. For a cat, it’s based on ideal weight at a fixed rate, because of the liver risk described above.

Should I feed my pet the same amount every day?

Any single day matters less than the average. But a fixed, measured amount each day is what makes the weigh-ins mean something. If the intake changes every day, you can’t tell what the scale is telling you.

Free calculators that do the arithmetic

• Dog calorie calculator, scaled by activity with the safety floor built in. It also gives grams from your food’s kcal per 100 g.
• Cat calorie calculator, using the ideal-weight maths and the safety floor for cats.

The app, Dog & Cat Nutrition Coach, starts from the same estimate and turns it into portions in grams, with a treat budget. Each week it adjusts the target from the meals and weigh-ins you log. It’s a nutrition and weight companion. It is not a medical device.

Method: resting energy requirement RER = 70 × (body weight in kg)^0.75, as used in the 2021 AAHA Nutrition and Weight Management Guidelines for Dogs and Cats and the WSAVA Global Nutrition Guidelines. The activity factors, weight-loss factors, safety floors and treat share are the ones the Dog & Cat Nutrition Coach app and calculators use. Last reviewed 30 September 2026.