Pet Food Portion Calculator
How much to feed a dog or cat each day, in grams and per meal, from its weight, life stage and the food's energy density — using the resting energy equation vets use.
Resting energy requirement (RER) = 70 × weight^0.
| Resting need (RER) | 662 |
|---|---|
| Daily need (MER) | 1,059 |
How the pet food portion calculator works
Resting energy requirement (RER) = 70 × weight^0.75 kcal a day. Multiply by the life-stage factor — a neutered adult dog 1.6, an active dog 2.5, a growing puppy up to 3.0; cats run lower — for the daily energy need (MER). Take off any treat allowance, then divide by the food's energy density (about 375 kcal per 100 g for dry food, 90 for wet) to get grams a day, and by the meals to get grams a meal. For weight loss, feed to the target weight.
Formula: RER = 70 × kg^0.75 · MER = RER × factor · grams/day = MER × (1 − treats%) × 100 ÷ kcal per 100 g · per meal = ÷ meals
How the daily amount is worked out
Energy first, then grams
Vets don't feed by weight, they feed by energy. First comes the Resting Energy Requirement — the calories an animal burns just existing: RER = 70 × bodyweight(kg)0.75 kcal/day. That resting figure is then scaled up by a life-stage factor to give the Maintenance (Daily) Energy Requirement, MER = RER × factor. Typical factors are about ×1.6 for a neutered adult dog and ×1.2 for a neutered adult cat, rising to ×2–3 for a growing puppy or kitten and higher again for hard-working dogs; for weight loss the RER is taken on the target weight and multiplied by about ×1.0 (dog) or ×0.8 (cat). Finally, calories become food: grams/day = MER × 100 ÷ the food's energy density (kcal/100 g). This is the WSAVA/AAHA global veterinary standard used in UK practice — the equation isn't country-specific, but the factor, your food's energy and the ideal weight all vary, so they're inputs.
Worked example
A neutered 20 kg dog: RER = 70 × 200.75 ≈ 662 kcal, then MER = 662 × 1.6 ≈ 1,059 kcal/day. On a typical dry food at 375 kcal/100 g that's 1,059 × 100 ÷ 375 ≈ 282 g of food a day — about 141 g per meal split over two meals. Switch to a wet food at ~90 kcal/100 g and the same dog needs roughly 1,177 g, because wet food is mostly water.
This is an estimate, not a prescription. Individual pets vary by breed, metabolism, health and neuter status. Weigh the food, watch the body condition score, and adjust every couple of weeks. Your vet's advice always overrides this tool — especially for puppies, kittens, pregnancy, illness or a weight-loss plan.
Life-stage & activity factorsWhy life stage changes the amount so much
The same bodyweight can need very different amounts of food depending on age, neuter status and how active the animal is. These are the typical MER factors applied to Resting Energy Requirement:
- Inactive / senior — ~×1.2–1.4. Older, quieter pets burn less; it's easy to keep feeding "adult" amounts and watch the weight creep on.
- Neutered adult — ~×1.6 dog, ×1.2 cat. Neutering lowers energy needs, so a neutered pet needs noticeably less than an entire one of the same weight. A 4 kg small dog lands at ≈317 kcal, about 84 g/day of 375 kcal/100 g dry food.
- Intact adult — ~×1.8 dog, ×1.4 cat. Entire animals run a little hotter.
- Active / working — ~×2–5 dog. A weekend agility dog sits near the bottom of that range; a full-time working or sled dog near the top. A 30 kg working dog at ×2.5 needs ≈2,243 kcal/day — roughly 598 g of dry food.
- Growth (under 4 months) — ~×3, then ~×2 (4–12 months). Puppies and kittens are building a body and need far more energy per kilo than adults. A 10 kg pup aged 4–12 months needs ≈787 kcal, about 197 g/day of a 400 kcal/100 g puppy food across three meals.
- Weight loss — RER on the target weight × ~1.0 dog / ×0.8 cat. A cat going from 5 kg to a 4 kg target works out at ≈42 g/day; a dog from 25 kg to 22 kg at ≈190 g/day. Weight gain for an underweight pet nudges the factor the other way.
Pick the row that matches your pet honestly — over-estimating activity is the most common way pets are quietly overfed. If your vet has given you a specific multiplier, enter it in the Detailed level to override the goal.
Food energy, labels & weighingFood energy, reading the label and weighing portions
Dry vs wet — it's all about water
A typical dry food holds about 375 kcal per 100 g; a typical wet food only about 90 kcal per 100 g, because it's roughly three-quarters water. To reach the same daily calories your pet needs about four times the weight of wet food — a 5 kg cat needing 281 kcal eats about 75 g of dry food or about 312 g of wet, for identical energy. Always compare foods on calories, not grams.
Reading a UK pet-food label
UK and European labels state metabolisable energy as kcal per kilogram, and some give kcal per 100 g directly, in line with FEDIAF nutritional guidelines. This calculator wants kcal per 100 g, so divide the kcal/kg figure by 10 — a food listed at 3,750 kcal/kg is 375 kcal/100 g. Enter your own food's number for the most accurate result: the figure varies a lot between products — dry roughly 300–450 and wet roughly 70–130 kcal/100 g — so premium and "light" foods can sit well above or below the defaults.
Weigh it, don't scoop it
Kitchen scales beat a measuring cup: studies have found cups can be out by 20–50%. Weigh the daily amount once, note where it sits in your scoop, and keep treats under about 10% of daily calories — treats count, and they add up fast. Then let the body condition score, not the bowl, be the final word: you should feel the ribs easily with a light cover, and see a waist from above.
Frequently asked Frequently asked questions
Where these figures come from
The method here is the mainstream veterinary-nutrition standard, not a country-specific rule. The energy equation and life-stage factors follow the WSAVA Global Nutrition Guidelines and AAHA feeding guidance used in UK practice; the food energy defaults are typical values you can replace with your own product's label figure.
- Resting Energy Requirement — RER = 70 × bodyweight(kg)^0.75 kcal/day (the standard allometric formula).
- Life-stage (MER) factors — neutered adult ~×1.6 (dog) / ×1.2 (cat); intact ~×1.8 / ×1.4; active/working ~×2–5; growth ~×3 then ~×2; weight loss RER on target weight ×~1.0 (dog) / ×0.8 (cat).
- Food energy density — typical dry food ~375 kcal/100 g, typical wet food ~90 kcal/100 g. UK and European labels state metabolisable energy as kcal/kg (some give kcal/100 g directly), in line with FEDIAF nutritional guidelines — divide kcal/kg by 10 for kcal/100 g.
- Treats — kept to ≤10% of daily calories, in line with standard veterinary advice.
- Further guidance — RSPCA — pet care guidance.
Last checked: July 2026. This is a planning estimate, not veterinary advice. Individual needs vary with breed, health, metabolism and neuter status — weigh the food, monitor body condition, and follow your own vet's recommendation, especially for puppies, kittens, pregnancy, illness or weight loss.
Understanding your resultSelect the question that matches where you are right now.
The headline number is the estimated amount of food to feed per day — grams, plus grams per meal — to meet your pet's daily calories (MER) on the food you chose. The breakdown shows the resting and daily calories behind it and how much each meal works out to.
What to do with itUse it as a starting point, weigh that amount, and split it across the meals you feed. Then check body condition every couple of weeks and nudge the amount up or down — the scales and the ribs are the real feedback, not the bowl.
What it is notIt's not veterinary advice or a fixed prescription. It doesn't account for illness, pregnancy, medications or an individual dog or cat's metabolism. For puppies, kittens, weight loss or any medical condition, feed to your vet's plan.
Why calories, not cupsFeeding by energy is how vets do it, because two foods of the same weight can differ hugely in calories. Enter your food's real kcal/100 g and the grams figure adjusts — a richer food means a smaller bowl.
Four things move the daily amount the most: bodyweight, life stage or goal, how active the pet is, and the food's energy density.
Weight & life stageRER scales with weight to the power 0.75, and the life-stage factor can nearly double the result — a growing puppy needs far more per kilo than a neutered senior of the same weight.
Food energyDry (~375 kcal/100 g) versus wet (~90) changes the grams roughly four-fold for the same calories. Always feed to your own food's label figure, not a generic gram amount.
Activity, treats & goalHonest activity matters — over-rating it is the classic overfeeding trap. Treats should stay under ~10% of daily calories, and a weight-loss goal feeds to the target weight, not today's weight, so the amount deliberately comes down.
A few habits keep the portion honest and your pet in good shape.
Weigh, don't scoopUse kitchen scales — cups can be out by 20–50%. Weigh the daily amount once and mark the level on your scoop so the whole household feeds the same.
Score the body, not the bowlYou should feel the ribs with a light cover and see a waist from above. If not, adjust by ~10% and re-check in two weeks — small, steady changes beat big swings.
Count the treatsChews, training treats and table scraps are calories too. Keep them under 10% of the daily total and take that energy off the meals so the sums still add up.
Pet food is one line in the household budget. Model the wider cost of a pet and how it fits your monthly outgoings.
How old is your dog?Life stage drives the feeding factor — check where your dog sits.
Dog age calculator → The whole householdSee how food and pet care fit your monthly running costs.
Cost of living → A buffer for the vet billBuild a rainy-day fund for the unexpected vet visit.
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How much to feed a 20 kg adult dog ≈ 282 g/day (dry food)
A neutered 20 kg adult dog needs about 1,059 kcal a day (RER 662 kcal × 1.6). On a typical premium dry food at 375 kcal/100 g that's about 282 g a day — roughly 141 g per meal across two meals. Always check YOUR bag's energy figure (AU labels show kcal/kg — divide by 10 for kcal/100 g) and adjust to body condition.
| Energy need (MER) | ≈1,059 kcal |
|---|---|
| Dry food/day | ≈282 g |
| Per meal | ≈141 g × 2 |
- Read the bag kcal/kg ÷ 10
- Weigh, don't scoop More accurate
How much to feed a 5 kg cat ≈ 75 g/day (dry food)
A neutered 5 kg cat needs about 281 kcal a day (RER 234 kcal × 1.2). On dry food at 375 kcal/100 g that's about 75 g a day — roughly 37 g per meal, twice a day. Cats do best with measured meals rather than a topped-up bowl; free-feeding kibble is a leading cause of feline obesity.
| Energy need (MER) | ≈281 kcal |
|---|---|
| Dry food/day | ≈75 g |
| Per meal | ≈37 g × 2 |
- Measured meals Beat free-feeding
- Neutered ×1.2 factor
Why wet food portions look huge Same cat: ≈ 312 g/day wet
That same 5 kg cat needing 281 kcal eats about 312 g a day of wet food — over four times the dry-food weight — simply because canned and pouch food is 75–85% water (~90 kcal/100 g) versus ~375 for kibble. The calorie need is identical; only the density changed. So never copy a dry-food gram figure onto wet food — match the portion to the energy on the tin.
| Wet density | ≈90 kcal/100 g |
|---|---|
| Dry density | ≈375 kcal/100 g |
| Wet food/day | ≈312 g |
- Same calories ~4× the weight
- Mixing? Split the calories
Puppy portions (10 kg, 4–12 months) ≈ 197 g/day, 3 meals
Growing dogs burn far more energy per kilo. A 10 kg pup aged 4–12 months uses a ×2.0 growth factor: RER 394 kcal × 2.0 = 787 kcal/day, or about 197 g of 400 kcal/100 g puppy dry food — split across three meals (~66 g each). Recheck the amount every couple of weeks as they grow, and use a puppy-formulated food, not adult.
| Growth factor | ×2.0 |
|---|---|
| Energy need | ≈787 kcal |
| Food/day | ≈197 g, 3 meals |
- Under 4 months ×3.0, 3–4 meals
- Reassess Every 2 weeks
Active or working dog (30 kg) ≈ 598 g/day
A hard-working 30 kg dog can need a ×2.5 factor (working dogs range 2.0–5.0). RER 897 kcal × 2.5 = about 2,244 kcal/day — roughly 598 g of 375 kcal/100 g dry food. Working and sporting dogs may need even more on heavy days; feed to maintain a lean, athletic body condition rather than to a fixed number.
| Activity factor | ×2.0–5.0 |
|---|---|
| Energy need | ≈2,244 kcal |
| Food/day | ≈598 g |
- Heavy work days Feed more
- Rest days Feed less
Feeding for weight loss Use the TARGET weight
The key nuance: a weight-loss plan is calculated on the ideal (target) weight, not the current weight. A cat now 5 kg but ideally 4 kg uses RER of 4 kg (198 kcal) × 0.8 = 158 kcal, about 42 g of dry food a day — well below its current maintenance. A dog from 25 kg to a 22 kg target uses ×1.0 on 22 kg ≈ 190 g/day, roughly a third less food. Always vet-supervise weight loss.
| Basis | Target weight |
|---|---|
| Cat 5→4 kg | ≈42 g/day |
| Dog 25→22 kg | ≈190 g/day |
- Slow & steady Vet-supervised
- Weigh food Don't eyeball
Small dog (4 kg) ≈ 84 g/day
A neutered 4 kg small-breed dog needs about 317 kcal a day (RER 198 × 1.6) — roughly 84 g of 375 kcal/100 g dry food, about 42 g per meal. Small breeds burn more energy per kilo than big dogs (the 0.75 exponent captures this), so don't just scale a big-dog portion down by weight — use the equation.
| Energy need | ≈317 kcal |
|---|---|
| Food/day | ≈84 g |
| Per meal | ≈42 g × 2 |
- Per-kilo need Higher than big dogs
- Toy breeds Watch for low blood sugar
Reading the energy off a pet-food label kcal/kg ÷ 10
UK and European pet-food labels state metabolisable energy as kcal/kg (some give kcal/100 g directly), in line with FEDIAF nutritional guidelines. To use it here, divide kcal/kg by 10: a food listed at 3,750 kcal/kg is 375 kcal/100 g. This single number — not the brand or the price — is what sets the portion, and it varies a lot (dry 300–450, wet 70–130). Type your bag's figure into the energy-density field for an accurate result.
| Label shows | kcal/kg (as fed) |
|---|---|
| Convert | ÷ 10 → kcal/100 g |
| Dry range | 300–450 kcal/100 g |
- Every food differs Always check
- No kcal on bag? Ask the maker
Worked examples
| Inputs | Food per day | Note |
|---|---|---|
| A 20 kg neutered dog on dry food, two meals | 282 g | RER 662 kcal, MER 1,059 kcal, 282 g a day |
| A 4 kg neutered cat on wet food | 264 g | about 264 g a day |
| Weight loss to a 25 kg target with 10% treats | 188 g | fed to the target weight at factor 1.0 |
FAQFrequently asked questions
How much should I feed my dog?
It depends on weight, life stage and activity, not just a number on the bag. Vets use the animal's Resting Energy Requirement — RER = 70 × bodyweight(kg)^0.75 kcal/day — then multiply by a life-stage factor: about 1.6 for a neutered adult, 1.8 for an intact adult, up to 2.0 or more for a working dog, and 2–3 for a growing puppy. A neutered 20 kg dog has an RER of about 662 kcal, so it needs roughly 1,059 kcal a day, which is about 282 g of a typical dry food at 375 kcal/100 g. Split it across two meals — about 141 g each — and adjust up or down every couple of weeks to keep a lean body condition.
How much should I feed my cat?
Cats need far fewer calories than their size suggests. Using RER = 70 × weight^0.75, a 5 kg cat has a resting need of about 234 kcal; with a factor of about 1.2 for a neutered indoor adult that gives roughly 281 kcal/day. On a dry food at 375 kcal/100 g that's only about 75 g — a small amount that's easy to overfeed. On a wet food at about 90 kcal/100 g the same 281 kcal is about 312 g. Growing kittens and pregnant or nursing queens need much more (a factor of 2–3). Weigh the food rather than free-pouring, and let body condition, not the bowl, guide the amount.
Why is the wet-food portion so much bigger than dry?
Because wet food is mostly water. A typical dry food packs about 375 kcal per 100 g, while wet food is only around 90 kcal per 100 g — roughly a quarter as dense. To hit the same daily calories your pet therefore needs about four times the weight of wet food: the 5 kg cat needing 281 kcal eats about 75 g of dry food or about 312 g of wet. The animal isn't eating more energy; it's eating more water. That's why the gram figure jumps when you switch the food type — always compare foods on calories, not grams.
How do I read the calories on a UK pet-food label?
UK and European labels state metabolisable energy as kcal per kilogram, and some give kcal per 100 g directly, in line with FEDIAF nutritional guidelines. This calculator asks for kcal per 100 g, so divide the kcal/kg figure by 10 — a food listed at 3,750 kcal/kg is 375 kcal/100 g. Once you have kcal/100 g, grams per day = daily calories × 100 ÷ energy density. The figure varies a lot between products (dry roughly 300–450, wet roughly 70–130 kcal/100 g), so always use your own bag's number rather than a generic one.
How do I feed my pet for weight loss?
Feed to the target (ideal) weight, not the current one, and go gently. A common vet approach bases the RER on the ideal weight and uses a factor of about 1.0 for dogs and 0.8 for cats. A cat now 5 kg but ideally 4 kg works out at about 158 kcal a day — roughly 42 g of dry food; a dog coming from 25 kg to a 22 kg target lands near 190 g/day, about a third less food. Keep treats under 10% of daily calories, weigh the food, and aim for slow loss — roughly 1–2% of bodyweight a week — with regular weigh-ins. Crash dieting is dangerous for cats in particular (risk of hepatic lipidosis), so always involve your vet in a weight-loss plan. Sources
The sources behind this calculator
- American Association of Feline Practitioners — Feline Life Stage Guidelines — the six feline life stages the cat-age page uses
- Wang et al. 2020, Cell Systems — Quantitative translation of dog-to-human aging by conserved remodeling of the DNA methylome — the 16·ln(age)+31 epigenetic formula on the dog-age page
- UK Government — Tips at work — the law on how tips are shared with staff
Last checked: September 2026. Where a page states a convention (a tipping custom, a pet life stage), the page names the body it follows.