Every number on PetPortions comes from a formula or a dataset you can inspect. This page documents both: how we turn a dog's weight and age into calories, how calories become cups and dollars, and where the underlying data comes from.
Step 1: calories per day
We start with the resting energy requirement (RER), the standard veterinary baseline for how much energy a dog burns at rest:
RER = 70 × (body weight in kg)0.75
Then we multiply RER by a maintenance factor that reflects life stage, activity, and body condition. This RER-times-multiplier approach follows National Research Council (NRC) calorie guidance, the same framework used in veterinary practice. These are the exact multipliers the calculator uses:
| Dog profile | Multiplier |
|---|---|
| Puppy under 4 months | 3.0 |
| Puppy, 4 to 12 months | 2.0 |
| Puppy of a large or giant breed, 12 to 24 months | 1.6 |
| Nursing (lactating) female | 3.0 |
| Pregnant female | 1.8 |
| Overweight dog | 1.2 |
| Senior dog | 1.2 |
| Adult, low activity | 1.2 |
| Adult, moderate activity | 1.4 |
| Adult, high activity | 1.6 |
| Adult, intact (not neutered or spayed) | add 0.2 to the activity multiplier |
Rules apply in the order listed: a nursing female uses 3.0 regardless of activity, and the intact adjustment applies only to healthy adults.
See the math step by step
Change the inputs and watch each step of the formula recalculate.
Example: 60 lb neutered adult, moderate activity, typical dry food.
For a result personalized to your dog's breed, age, and activity, use the full calculator.
Estimates only, not veterinary advice.
A few definitions the calculator applies automatically:
- A dog counts as a puppy under 12 months of age, or under 24 months for large and giant breeds, which mature more slowly.
- A dog counts as a senior past 7 years, or past 5 years for giant breeds.
- If you pick a breed, we use its typical size category; the Mixed Breed option relies on the weight you enter.
Worked example. A 50 lb (22.7 kg) neutered adult with moderate activity: RER = 70 × 22.70.75 ≈ 727 kcal. The moderate-activity multiplier of 1.4 gives a daily target of about 1,018 kcal.
Step 2: calories become cups and grams
For dry food we divide the daily calorie target by the food's energy density, taken from the manufacturer's published numbers:
- grams per day = daily kcal ÷ kcal per kg × 1000
- cups per day = daily kcal ÷ kcal per cup
Two foods can differ by 25% or more in calories per cup, which is why "one scoop" is not a portion. If a manufacturer does not publish complete calorie and nutrition data for a product, that product is left out of the calculator's results rather than filled in with a guess.
Step 3: cups become dollars
For each dry food we take the largest in-stock bag with a known retailer price and compute:
- days per bag = bag weight ÷ grams per day
- monthly cost = 30 ÷ days per bag × bag price
- cost per day = monthly cost ÷ 30
Prices are public retailer prices recorded in periodic snapshots. Prices move, so treat cost per day as an estimate of the right magnitude, not a live quote. Each result card shows which bag size the math is based on.
Fresh subscription foods (The Farmer's Dog, Ollie, Nom Nom, Spot & Tango) price by dog profile rather than by bag, so we show their published price ranges for your dog's size bucket instead of computing portions.
The data behind the calculator
- 249 breeds with size categories, plus a mixed-breed option
- Nearly 200 foods from 16 brands, dry and fresh
- Nutrition figures from manufacturers' guaranteed analysis and feeding data
- Retailer prices in periodic snapshots
What this model does not cover
The calculator is a mathematical model of an average healthy dog. It does not account for medical conditions, weight-loss programs, extreme working loads, or individual metabolism, and pregnancy and nursing estimates are especially rough because needs vary by stage and litter size. Start with our number, watch your dog's body condition for a few weeks, and adjust. For anything medical, your vet has the final word.
Try it on your own dog
Every formula on this page is exactly what the calculator on the homepage runs for your inputs. Pick your dog's weight and food, and you will see these numbers applied: RER, the life-stage multiplier, calories per cup, and the resulting daily portion and cost.