The key point: the calculator result is a first estimate of daily calories, not a guaranteed portion size. Actual needs are checked by monitoring body weight, body condition score (BCS), and the animal’s wellbeing, then adjusting the portion over time.
RER, MER, and DER in plain language
RER, or resting energy requirement, describes the energy the body needs at rest. One commonly used equation is:
RER = 70 × body weight (kg)0.75 [kcal/day]
The 0.75 exponent accounts for the fact that energy needs do not rise in direct proportion to kilograms. It is still an equation-based estimate, not a measurement of an individual animal [1] [2].
MER, or maintenance energy requirement, is the energy needed to maintain energy balance and a stable body weight. DER, or daily energy requirement, is a term used in calculators and guides for a daily target. These labels are not applied identically everywhere. In practice, the interpretation matters more than the acronym: this is an initial daily target that must be checked through observation.
Why one multiplier does not fit every animal
Activity, neuter status, body condition, life stage, environmental temperature, and health can all affect energy needs. That does not mean each factor has one fixed, universal multiplier that can always be safely multiplied by all the others.
WSAVA’s tables for healthy adult animals illustrate this. As reference equations for estimating daily energy, they give dogs 95 × body weight (kg)0.75 [kcal/day] at low activity and 130 × body weight (kg)0.75 [kcal/day] at higher activity [3]. For cats, they use different equations and exponents: 100 × body weight (kg)0.67 [kcal/day] for lean cats and 130 × body weight (kg)0.4 [kcal/day] for obesity-prone cats [4]. These are starting references for further assessment, not measurements of an individual animal’s needs.
The calculator above combines the entered information into a simplified estimate. Its fields should not be treated as a set of independent clinical prescriptions. Senior status alone also does not prove that an animal needs fewer calories: research shows wide variation between individuals, and body weight or age alone cannot reliably predict energy needs [7] [8].
For puppies and kittens, and during pregnancy or lactation, needs change with growth stage, week of pregnancy or lactation, and litter size. In these situations, as well as with illness or a planned weight-loss programme, the feeding plan and calculator result should be discussed with a veterinarian; the WSAVA nutritional assessment guidelines identify these factors as reasons for extended evaluation [2].
How to convert calories into grams
You need the calorie density of the actual diet to calculate a weight of food:
portion (g/day) = energy target (kcal/day) ÷ calorie density (kcal/100 g) × 100
If the target is 500 kcal and the diet provides 200 kcal per 100 g, the initial portion is 250 g. All calorie-containing treats and supplements should be included in the daily total. WSAVA advises treating a portion calculated this way as a starting point, not a final answer [5].
Why the “2–3% of body weight” rule can mislead
A body-weight percentage tells you how much food to weigh, but not how much energy that portion contains. For a 10 kg dog, a 2% rule gives 200 g of food. That same weight provides:
- 240 kcal when the diet contains 120 kcal/100 g,
- 480 kcal when the diet contains 240 kcal/100 g.
The energy intake doubles even though the body-weight percentage does not change. An energy-based calculation therefore includes an important piece of information that the percentage rule misses. It, too, remains an estimate that must be monitored.
BCS and body weight show whether the portion works
WSAVA notes that actual needs may differ from a calculated starting point by about 30% in either direction for dogs and as much as 50% for cats [2]. A difference may reflect natural variation, but it can also result from the equation’s limitations or inaccurate inputs. The estimate therefore has to be checked against the animal’s response.
After starting the portion:
- weigh the animal regularly, ideally under similar conditions,
- assess BCS on the same 9-point scale; the target for most dogs and cats is 4–5/9 [6],
- monitor muscle condition, activity, appetite, and digestive signs,
- initially review the trend about every two weeks and adjust the portion gradually [5].
If weight changes quickly, BCS is clearly outside 4–5/9, or the animal has a medical condition, a veterinarian should set the feeding plan and rate of change [2].
What this means in BARFLAB
The BARFLAB calculator helps set an initial daily energy target from the information provided. Comparing it with the diet’s calorie density gives a portion in grams. The result does not guarantee the right portion for an individual dog or cat: the right portion is the one that helps maintain the intended weight and body condition over time without unwanted signs.
Sources
- National Research Council (2006). Nutrient Requirements of Dogs and Cats. The National Academies Press. https://doi.org/10.17226/10668
- WSAVA Global Nutrition Committee (2011). Nutritional Assessment Guidelines. WSAVA publication, DOI
- WSAVA Global Nutrition Committee (2020). Calorie Needs for Healthy Adult Dogs. WSAVA publication
- WSAVA Global Nutrition Committee (2020). Calorie Needs for Healthy Adult Cats. WSAVA publication
- WSAVA Global Nutrition Committee. Frequently Asked Questions and Myths. WSAVA publication
- WSAVA Global Nutrition Committee (2025). Body Condition Score. BCS chart for dogs and cats
- Bermingham et al. (2014). Energy Requirements of Adult Dogs: A Meta-Analysis. PLOS ONE. https://doi.org/10.1371/journal.pone.0109681
- Bermingham et al. (2010). Energy Requirements of Adult Cats. British Journal of Nutrition. https://doi.org/10.1017/S000711450999290X