"Serve half a cup a day" only works if you know how many calories are in that cup — and
every food is different. The reliable way is to start from your cat's daily calorie need
and divide by your food's calories per cup. Enter your cat's weight, life stage, and the
kcal-per-cup from your bag below to get daily calories and cups per day. Everything here
follows the standard veterinary RER/MER energy-requirement method.
Calories first, then cups·7 life-stage factors·Standard RER/MER formula
Read this first
This is an estimate from the standard RER/MER formula, not veterinary advice. Your cat's
real needs depend on body condition score, breed, metabolism, spay/neuter status, and
health conditions, and no calculator is exact. Confirm the amount with your veterinarian
and follow your food's feeding guide. Never cut a cat's food sharply without veterinary
guidance — sudden calorie restriction can cause hepatic lipidosis (fatty liver disease).
Enter your cat's weight, pick the life stage that fits, and enter your food's calories per cup (printed on the bag as "ME kcal/cup"). You'll get daily calories and cups per day.
Use your cat's current weight — or target weight if feeding for weight loss.
The factor multiplies resting energy to reach the daily total.
Default 300. Find the exact "ME kcal/cup" on your food's bag or the maker's site. Dry cat foods often run 280–450.
Daily calories (MER)
Cups per day
Resting energy (RER)
Life-stage factor
Per meal (twice daily)
The math, honestly
How the calculation works (RER & MER)
Vets don't start from cups — they start from calories. The first
number is the resting energy requirement (RER): the energy a cat burns at rest. It
scales with body weight in kilograms, raised to the three-quarter power, because
smaller animals burn more energy per pound than larger ones.
RER = 70 × (weight in kg)0.75
Then RER is multiplied by a life-stage factor for the cat's age and
reproductive status to get the maintenance energy requirement (MER) — the daily calorie
target. A typical neutered adult uses 1.2; a young kitten in its fastest growth phase
needs up to 2.5.
MER (daily calories) = RER × life-stage factor
Finally, divide daily calories by your food's calories per cup to
translate calories into a real serving. Two foods for the same cat can require very
different cup amounts, which is why a fixed "half a cup" rule of thumb so often misses.
cups per day = daily calories ÷ kcal per cup
Worked example: a 10 lb (about 4.54 kg) neutered adult. RER = 70 ×
4.540.75 ≈ 218 kcal; MER = 218 × 1.2 ≈ 261 kcal/day;
on a food with 300 kcal per cup that's about 0.9 cups per day,
usually split into two meals.
Life-stage factors
The life-stage factor is the multiplier applied to resting energy. These are the standard
published values used in small-animal nutrition for cats. Pick the one that best matches
your cat; when two seem to fit, start lower and adjust by body condition.
Life stage
Factor× resting energy
Notes
Weight loss
0.8
Calculate at the cat's target weight, not current. Do not cut sharply — consult your vet.
Senior / inactive
1.0
Older or very sedentary cats with reduced energy needs.
Neutered adult
1.2
The most common everyday case for indoor adult cats.
Intact adult
1.4
Slightly higher needs than a neutered cat.
Weight gain
1.8
Underweight cats needing to put on condition.
Kitten, 4–12 months
2.0
Still growing; approaching adult size.
Kitten, 0–4 months
2.5
Fastest growth phase; portions change often.
Factors are standard published multipliers and represent typical cases. Individual cats
vary with metabolism, breed, and health, so treat the result as a starting estimate and
tune it to your cat's body condition with your veterinarian.
Example daily calories by weight
Daily calories (MER) and cups per day for a typical neutered adult
(factor 1.2) at a few weights, assuming a food with 300 calories per cup. Find a weight
close to your cat's, but use the calculator above for your cat's actual numbers.
Weight
Resting energyRER, kcal
Daily caloriesMER, ×1.2
Cups per dayat 300 kcal/cup
6 lb · 2.7 kg
154
185
0.6
8 lb · 3.6 kg
192
231
0.8
10 lb · 4.5 kg
218
261
0.9
12 lb · 5.4 kg
250
300
1.0
14 lb · 6.4 kg
282
338
1.1
16 lb · 7.3 kg
312
374
1.2
18 lb · 8.2 kg
341
410
1.4
Calories are rounded to whole numbers and cups to one decimal. These assume a neutered
adult on a 300 kcal/cup food; a denser food means fewer cups and a lighter food means
more, so always read your own bag's calories-per-cup figure.
The three steps, in plain terms
The whole method comes down to three moves: find resting energy, scale it for the cat,
then convert calories into cups using your food.
Step 1
Resting energy
Convert weight to kilograms and compute RER = 70 × kg0.75. This is the baseline energy a cat burns just existing, before any activity.
Step 2
Scale for the cat
Multiply RER by the life-stage factor — 1.2 for a neutered adult, up to 2.5 for a young kitten — to get daily calories (MER).
Step 3
Calories to cups
Divide daily calories by your food's calories per cup. Split the total across the meals you feed — most cats do well on two meals a day.
Then
Tune by condition
Re-check against body condition score: ribs easy to feel, a visible waist from above. Adjust the amount up or down and confirm with your veterinarian.
Cat feeding glossary
The terms behind the calculator, in plain English. Definitions reflect standard
small-animal nutrition usage — they are background, not advice.
Resting energy requirement (RER)
The calories a cat needs at complete rest, in a comfortable environment, neither growing nor exercising. Calculated as 70 × body weight in kilograms to the 0.75 power. RER is the foundation every other feeding number is built on.
Maintenance energy requirement (MER)
The full daily calorie need once life stage and reproductive status are accounted for. It equals RER multiplied by a life-stage factor. MER is the number you actually feed to.
Life-stage factor
A multiplier applied to resting energy to reflect how much more than rest a cat needs — for example 1.2 for a neutered adult, 2.0 for a growing kitten, or 0.8 for a cat on a supervised weight-loss plan. These are standard published values, not exact measurements for any individual cat.
Calories per cup (ME kcal/cup)
The metabolizable energy in one cup of a specific food, printed on the bag. Because foods differ widely — roughly 280 to 450 calories per cup for many dry cat foods — the same cat needs a different number of cups depending on the food. Always use your own bag's figure.
Body condition score (BCS)
A hands-on assessment of whether a cat is at a healthy weight, usually on a 1–9 scale where about 4–5 is ideal. You should be able to feel the ribs easily without pressing hard, and see a gentle waist taper from above. BCS is the practical check that tells you whether the calculated amount is actually right.
Metabolizable energy (ME)
The energy in a food that a cat can actually absorb and use, after losses in feces and urine. It is the basis for the calories-per-cup figure on pet food labels and the number this calculator divides into the daily calorie target.
Spay / neuter status
Whether a cat has been surgically sterilized. Neutered and spayed cats tend to have lower energy needs, which is why the neutered-adult factor (1.2) is below the intact-adult factor (1.4). Indoor neutered cats are particularly prone to weight gain when overfed.
Hepatic lipidosis
A potentially life-threatening liver condition in cats caused by rapid calorie restriction. Unlike dogs, cats should never have food sharply cut without veterinary guidance. Any weight-loss plan for a cat should be gradual and supervised.
Frequently asked
Start from your cat's daily calorie need, not a fixed cup amount. The standard veterinary method is to calculate resting energy (RER = 70 × body weight in kilograms to the 0.75 power), then multiply by a life-stage factor — about 1.2 for a typical neutered adult or 2.0 for a kitten four to twelve months old. That gives daily calories (MER). Divide by your food's calories per cup to get cups per day. The calculator above does all of this. It's an estimate — confirm the amount with your veterinarian and follow your food's feeding guide.
Cups per day depends on two numbers: your cat's daily calorie need and how many calories are in one cup of your food. A 10 lb (about 4.5 kg) neutered adult needs roughly 261 calories a day, so on a food with 300 calories per cup that's about 0.9 cups daily, usually split into two meals. A more calorie-dense food means fewer cups; a lighter food means more. Always read the calories-per-cup figure off your own bag rather than assuming.
Three steps. First, find resting energy: RER = 70 × (weight in kg) to the power of 0.75. Second, multiply by a life-stage factor — common values are 1.2 for a neutered adult, 1.4 for an intact adult, 0.8 for weight loss, 1.8 for weight gain, 2.5 for a kitten under four months, 2.0 for a kitten four to twelve months, and 1.0 for a senior or inactive cat. That product is the daily maintenance energy requirement (MER) in calories. Third, divide daily calories by your food's calories per cup to get cups per day, then split that across the meals you feed.
Look on the bag or the manufacturer's website for a metabolizable energy figure, usually printed as "ME" and given as kcal per cup or kcal per kilogram. The kcal-per-cup number is the one this calculator uses. If your bag only lists kcal per kilogram of food, you'll need the cup weight to convert, so it's easiest to use the per-cup value. Dry cat foods commonly run from about 280 to 450 calories per cup.
Kittens need far more energy per pound than adults because they're growing rapidly. Veterinary feeding factors are roughly 2.5 times resting energy for kittens under four months, then about 2.0 from four to twelve months, compared with about 1.2 for a typical neutered adult. Because kittens grow quickly, their portions change often, so weigh regularly and adjust. Use a food formulated for growth or for all life stages, and confirm amounts with your veterinarian.
For weight loss, vets typically calculate resting energy at the cat's target (ideal) weight and apply a factor of about 0.8. This calculator's "weight loss" option does that; enter your cat's target weight, not its current weight. Weight loss in cats must be gradual — rapid restriction can cause hepatic lipidosis (fatty liver disease), which is potentially life-threatening. A vet-guided plan with regular weigh-ins is strongly recommended.
RER stands for resting energy requirement — the calories a cat needs at rest — and is calculated as RER = 70 × (body weight in kilograms) raised to the 0.75 power. MER stands for maintenance energy requirement and is the RER multiplied by a life-stage factor that reflects age and reproductive status. This is the established small-animal nutrition method. The life-stage factors are standard published multipliers, but every cat is different, so the result is a starting estimate to refine with your vet using body condition score.
Common mistakes with this calculator
Applying dog activity factors to a cat
Cats and dogs have different metabolic profiles. A neutered adult cat uses a factor of about 1.2; a neutered adult dog uses about 1.6. Using the dog multiplier on a cat overshoots daily calories by roughly 33%. Chronic overfeeding is the leading cause of obesity in pet cats, and the activity factor is where this mistake most often enters the calculation.
Not reading the actual kcal/cup off the label
Dry cat foods range from roughly 280 to 450 kcal/cup. Wet foods are far more dilute because they're 75–85% water, so kcal-per-volume comparisons between dry and wet are meaningless. The metabolizable energy (ME) figure is on every product label or the manufacturer's site. Skipping this step and using a generic average can throw cup count off by 30–50%.
Cutting food too sharply for weight loss
Cats can develop hepatic lipidosis (fatty liver disease) when they stop eating — a complete loss of appetite for a few days is the real trigger in an overweight cat, which is exactly why a crash diet is dangerous. Gradual, vet-supervised reduction is safe; the risk comes from a cat that refuses food, not from a careful plan. The standard veterinary approach is a gradual reduction, calculating RER at the target weight with a factor of about 0.8, done under vet supervision with regular weigh-ins. Do not simply halve portions. This is not veterinary advice — consult your vet before starting any weight-loss plan.
Not adjusting after spay or neuter
Neutering reduces a cat's energy needs noticeably. The factor drops from about 1.4 (intact adult) to about 1.2 (neutered adult) — roughly a 14% reduction. Many owners continue the pre-neuter amount and see steady weight gain over the following months. Recalculate using the neutered-adult factor within a few weeks of the procedure.