Dog/Cat Daily Food Portion

Turning Species, Weight, and Activity Level Into a Daily Calorie Target

Resting Energy Requirement (RER) is the calories an animal needs at rest, calculated from body weight; multiplying by a species-specific activity factor gives Daily Energy Requirement (DER) — the calories your pet needs each day. Dogs and cats genuinely need different activity-factor multipliers at the same activity level — a cat’s maintenance energy needs are lower per pound of body weight than a dog’s — so select the correct species along with body weight and activity level to find both figures.

The Formula

$$\vC{\text{RER}} = 70 \times \vA{\text{Weight (kg)}}^{0.75}$$ $$\vD{\text{DER}} = \vC{\text{RER}} \times \vB{\text{Activity Factor}}$$

Per the Merck Veterinary Manual’s published maintenance-energy table, the activity factor for a dog is 1.4 for Weight Loss, 1.6 for Normal, or 1.8 for Active; for a cat it’s 1.0 for Weight Loss, 1.2 for Normal, or 1.4 for Active.

Worked Example

A 20 kg, Normal-activity dog:

1. RER: $\vC{\text{RER}} = 70 \times \vA{20}^{0.75} \approx \vC{662} \text{ kcal}$.
2. DER: $\vD{\text{DER}} = \vC{662} \times \vB{1.6} \approx \vD{1,059} \text{ kcal/day}$.

A 4 kg, Normal-activity cat, for comparison:

1. RER: $\vC{\text{RER}} = 70 \times \vA{4}^{0.75} \approx \vC{198} \text{ kcal}$.
2. DER: $\vD{\text{DER}} = \vC{198} \times \vB{1.2} \approx \vD{238} \text{ kcal/day}$.

Note the cat’s DER multiplier (1.2x) is noticeably lower than the dog’s (1.6x) at the same “Normal” activity label — using a dog’s multiplier for a cat would overstate its true calorie needs by roughly a third.

Key Factors to Consider

• Always double-check the species selection before reading the result. The activity-factor table is genuinely different for dogs and cats — picking the wrong species silently applies the other animal’s multiplier and can meaningfully over- or under-estimate the calorie target.
• This estimates a starting calorie target, not a precise prescription for every pet. Age, spay/neuter status, breed, and individual metabolism all affect real calorie needs — a pet’s actual ideal intake should be adjusted based on how their body condition changes over a few weeks, not treated as a fixed number forever.
• Once you know the DER, converting to actual food quantity requires checking the specific food’s own calorie density. Different pet foods pack meaningfully different calories per cup or per can — the kcal/day figure this calculator produces needs to be divided by the specific product’s own stated kcal-per-serving to find how much to actually feed, which varies brand to brand.
• A pet’s activity level can change meaningfully with age, health status, or season, and DER should be revisited when it does. A previously Active dog that becomes less mobile due to age or an injury may need to shift toward the Normal or Weight Loss activity factor to avoid unintended weight gain.
• Body condition scoring (checking rib visibility/feel and waist definition) is the practical way to confirm a calorie target is actually working. Regularly checking body condition, rather than relying on the calculated number alone, is the standard veterinary-recommended way to confirm a feeding amount is keeping a pet at a healthy weight.

Common Mistakes

• Using a dog’s activity factor for a cat, or vice versa. The two species have genuinely different DER multipliers at every activity level — a cat is not just a small dog for the purposes of this formula.
• Treating the DER figure as the number of cups or cans to feed. This calculator gives a calorie target, not a food volume — you still need to check your specific food’s own calories-per-serving to convert it into an actual amount.
• Never revisiting the activity factor as circumstances change. A pet’s real activity level shifts with age, injury, or a change in routine, and using an outdated activity factor can silently over- or under-feed a pet for months.
• Ignoring visible weight trends in favor of the calculated number. The formula is a starting estimate — if a pet is visibly gaining or losing weight at the calculated calorie level, adjust the actual amount fed rather than treating the number as fixed.

Useful to Know

• Want to see how your pet’s age converts to a human-year equivalent alongside its calorie needs? Pet Age Calculator converts dog or cat age using published veterinary age charts.
• Curious what your pet’s food and care will cost over its expected lifetime? Lifetime Cost of Pet Ownership Calculator projects total lifetime spending on food, vet care, and supplies.
• Want to factor exercise into your pet’s overall energy balance? Dog Walk Calories Calculator estimates calories burned on a walk based on distance, pace, and weight.