What this calculator does
Daily calorie needs are built in two steps. Resting energy requirement is 70 multiplied by body weight in kilograms raised to the power 0.75, which gives what the animal burns doing nothing. Maintenance energy requirement multiplies that by an activity factor, typically 1.2 to 2.0 depending on life stage and how much the animal actually does.
The power of 0.75 is the part that matters and the part most rules of thumb miss. Energy needs do not scale in proportion to weight, so a 40 kg dog does not need twice what a 20 kg dog needs. It needs about 1.7 times as much. Feeding by simple proportion overfeeds large animals and underfeeds small ones.
The formula
Resting energy is 70 times body weight in kilograms to the power of 0.75. That figure is multiplied by the activity factor for the life stage selected to give the daily maintenance requirement. The per-meal figure simply halves the daily total for twice-daily feeding. These are starting estimates from standard veterinary nutrition formulas, not prescriptions.
| Term | Meaning |
|---|---|
| RER | Resting energy requirement: what the animal burns at rest, before any activity. |
| MER | Maintenance energy requirement: RER multiplied by an activity factor, and the figure to feed to. |
| Activity factor | A multiplier from about 1.0 for weight loss up to 3.0 for a young puppy or kitten. |
| Metabolic weight | Body weight raised to the power 0.75, which is what energy needs actually scale with. |
The inputs explained
| Field | What to enter |
|---|---|
| Body weight (kg) | Body weight in kilograms. Use the animal current weight, or its ideal weight if the goal is weight loss. |
| Life stage / activity | The activity factor matching the life stage and activity level. Neutering lowers requirements noticeably, which is why it has its own band. |
When to use it
Setting a starting point for feeding
Package guidelines are generic and often generous. Calculating from body weight and activity gives a starting figure to adjust from based on what actually happens to the animal weight.
Managing weight gain
The weight-loss activity factor of 1.0 is calculated against ideal weight rather than current weight, and any weight-loss plan is worth discussing with a vet before starting.
Feeding a working or very active animal
A working dog can need double what a neutered house dog of the same size needs, which is a difference far too large to handle by eye.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How many calories does a dog or cat need per day?
A range of body weights at the same activity factor, showing how needs scale.
| Body weight | Daily calories (MER) | Resting energy (RER) | Per meal, fed twice daily |
|---|---|---|---|
| 5 kg | 374 kcal/day | 234 kcal/day | 187 kcal |
| 10 kg | 630 kcal/day | 394 kcal/day | 315 kcal |
| 20 kg | 1,059 kcal/day | 662 kcal/day | 530 kcal |
| 30 kg | 1,436 kcal/day | 897 kcal/day | 718 kcal |
| 45 kg | 1,946 kcal/day | 1,216 kcal/day | 973 kcal |
Questions
Why is body weight raised to the power 0.75?
Because metabolic rate scales with roughly the three-quarter power of body mass across animals, a relationship known as Kleiber law. Larger bodies are more efficient per kilogram, so energy needs rise more slowly than weight does. It is why feeding charts are curves rather than straight lines.
Should I use current or ideal weight?
Ideal weight, if the animal is overweight and the goal is to reduce. Calculating against current weight feeds to maintain the current state. Any deliberate weight-loss plan is worth setting with a vet, who can set a safe rate and check there is nothing else going on.
How does this compare to what the food packet says?
Packet guidelines are broad ranges covering many animals and tend towards the generous end. The calculated figure is a better starting point, but either way what matters is what happens over the following weeks: body condition and weight trend are the real feedback.
Does neutering really change the requirement?
Yes, noticeably. Neutered animals typically need somewhere around 20 to 30% fewer calories than intact ones of the same weight, which is why post-neutering weight gain is so common when feeding carries on unchanged.
For how much food that translates into by weight, see the dog daily food calculator. For daily water, see the dog water intake calculator.