Feeding a cat by the picture on the bag is how cats quietly gain a pound a year. The bag’s chart assumes an average cat living an average life; your cat has a specific weight, age, and neuter status, and each of those changes the right number of calories. This cat calorie calculator uses the veterinary standard method — resting energy requirement scaled by a life-stage factor — to give you a daily calorie target and the grams of food that deliver it.
The Two Numbers Behind Cat Feeding: RER and DER
Veterinary nutrition starts with resting energy requirement: RER = 70 × (body weight in kg)^0.75. The three-quarter power is not arbitrary — across species, metabolic rate scales with body mass to the 0.75 power, which is why a cat twice as heavy does not need twice the food. RER is the energy a cat burns at complete rest in a comfortable temperature. Real life costs more, so RER is multiplied by a daily energy requirement (DER) factor for the cat’s situation: growth, reproduction, activity, and neuter status all move the factor. This calculator applies both steps and then converts the calorie answer into grams of the food you actually feed.
DER Factors, Explained
Neutered adult ×1.2 — the default pet cat; neutering lowers metabolic rate and raises appetite, the combination behind most indoor weight gain. Intact adult ×1.4 — unneutered cats burn more and roam more. Indoor, low activity ×1.0 — some sedentary cats maintain weight on RER alone. Senior ×1.1 — older cats absorb nutrients less efficiently even as activity falls. Kittens ×2.0 to ×2.5 — growth is expensive; young kittens need two and a half times their resting rate. Weight loss ×0.8 — calculated at the cat’s ideal weight, not current weight, under veterinary supervision.
Worked Example: A 4.5 kg Neutered Cat
For a 4.5 kg cat, RER = 70 × 4.5^0.75 = 70 × 3.09 = 216 kcal. As a neutered adult, DER = 216 × 1.2 = 260 kcal per day. On a typical dry food at 350 kcal per 100 g, that is about 74 g of food daily — visibly less than most owners pour by eye, which is exactly why the calculation matters. Switch the same cat to intact status and the target rises to 303 kcal; drop to the weight-loss factor at ideal weight and it falls near 173 kcal.
From Calories to the Bowl
Find your food’s energy density on the label — it is printed as kcal/kg, kcal per cup, or kcal per 100 g; divide kcal/kg by 10 to get kcal per 100 g. Weigh the day’s food on a kitchen scale rather than using a cup: a “cup” of kibble can vary by 25 percent between scoops. Count treats inside the budget — a common rule is that treats should stay under 10 percent of daily calories, about 26 kcal for our example cat, which is roughly a small handful of standard treats. Wet food is far less dense (often 70 to 100 kcal per 100 g), so the same 260 kcal target can mean 260 to 370 g of wet food — the calculator’s density field handles the conversion.
Adjusting Over Time
The calculator gives a starting point, not a verdict. Weigh your cat every two weeks and score body condition: ribs should be felt under a thin fat cover, with a visible waist from above. If weight climbs for a month, trim the target by about 10 percent; if it falls unintentionally, raise it. Sudden appetite or weight changes, especially in seniors, are a reason for a vet visit rather than a bigger or smaller bowl — hyperthyroidism, diabetes, and kidney disease all announce themselves at the scale first.
Common Mistakes
Feeding for the weight the cat is when the goal is the weight it should be locks in the excess. Free-feeding dry food makes any calorie plan fiction. Forgetting that neutered cats need less than the bag chart assumes is the single most common error. And using the linear 30 × kg + 70 shortcut is acceptable for mid-size cats but drifts at very small or large weights — the 0.75-power formula in this calculator is the more accurate standard.
Related Tools
More pet tools live in the Biology Calculators hub — see the Dog Crate Size Calculator and the Horse Weight Calculator.
Frequently Asked Questions
How many calories does a cat need per day?
A typical 4.5 kg (10 lb) neutered indoor cat needs about 260 kcal per day. The exact figure is RER (70 × kg^0.75) times a life-stage factor — 216 kcal resting, scaled to roughly 220 to 300 kcal for most adult pets.
What is RER for cats?
Resting energy requirement: the calories a cat burns at rest, calculated as 70 × (weight in kg)^0.75. A 4 kg cat has an RER of about 198 kcal; a 5 kg cat about 234 kcal.
Why do neutered cats need fewer calories?
Neutering reduces metabolic rate and roaming while increasing appetite. The standard DER factor drops from 1.4 (intact) to 1.2 (neutered), about a 15 percent reduction in daily calories.
How many calories should a kitten eat?
Kittens need 2 to 2.5 times their RER — the calculator’s kitten factors. A 1 kg young kitten has an RER of 70 kcal and a target near 175 kcal per day, rising with weight as it grows.
How do I put my cat on a diet safely?
Feed the weight-loss DER: 0.8 × RER at the cat’s ideal weight, weigh every two weeks, and aim for about 0.5 to 1 percent of body weight lost per week. Never fast an overweight cat — rapid food restriction risks hepatic lipidosis, a serious liver condition.
Are treats included in the daily calorie count?
Yes. Everything the cat eats counts. Keep treats under about 10 percent of the daily target and subtract them from the food portion.
Why is wet food measured so differently from dry?
Water weight. Wet food is typically 70 to 100 kcal per 100 g; dry food 320 to 400. The same calorie target therefore means three to four times the grams in wet food — enter your food’s actual density in the calculator.