Tell us what you are feeding, how heavy it is, and how long you will be gone. We work out the hopper size, the meals per day and the backup power your gear actually needs — before you buy the wrong thing.
How long can you leave a dog or cat alone?
This is a ceiling, not a target. An automatic feeder keeps the routine going — it cannot notice a blockage, a spill, or a pet that has quietly stopped eating. The calculator applies these same numbers.
| Pet | Safe with no visit | What the setup still needs |
|---|---|---|
| Dog | Up to 1 day | A feeder with battery backup for any trip of 1 day or more. Dogs need a toilet break, exercise and human contact daily, so this ceiling is low on purpose. |
| Cat | Up to 3 days | Battery backup, a camera from 2 days so you can confirm meals actually dropped, and a self-cleaning box from 2 days. Cats hide illness, so only count on this if you have tested the whole setup beforehand. |
| Any pet | 4 days or more: no | Past this point the question stops being about equipment and becomes about who physically checks on them. Book at least one drop-in visit, or boarding. |
Daily food and water needs by weight
Dry food as a percentage of body weight, stepped by size — a small dog burns far more energy per kilogram than a large one, so a single percentage would underfeed the little one. Water is millilitres per kilogram.
| Pet | Weight | Dry food per day | Water per day | Meals per day |
|---|---|---|---|---|
| Small dog | 3 kg | 105 g 3.5% of body weight | 165 ml | 2 |
| Medium dog | 10 kg | 300 g 3.0% of body weight | 550 ml | 2 |
| Large dog | 22 kg | 572 g 2.6% of body weight | 1,210 ml | 2 |
| Giant dog | 40 kg | 880 g 2.2% of body weight | 2,200 ml | 2 |
| Adult cat | 4 kg | 80 g 2.0% of body weight | 200 ml | 3 |
Maintenance averages for a healthy adult pet on dry food. Activity, age, neutering and body condition all move the number, so treat it as a starting point rather than a prescription.
Feeder and fountain capacity for a 3-day trip
Daily need multiplied by the days away, then rounded up with a safety margin: 25% on the hopper for spills and portion drift, 30% on the fountain for evaporation and splashing.
| Pet | Weight | Hopper capacity | Fountain capacity |
|---|---|---|---|
| Small dog | 3 kg | ≥ 400 g | ≥ 0.7 L |
| Medium dog | 10 kg | ≥ 1,130 g | ≥ 2.2 L |
| Large dog | 22 kg | ≥ 2,150 g | ≥ 4.8 L |
| Giant dog | 40 kg | ≥ 3,300 g | ≥ 8.6 L |
| Adult cat | 4 kg | ≥ 300 g | ≥ 0.8 L |
This assumes the equipment covers the whole trip. If someone is visiting daily they can refill, and a smaller hopper is enough — but never size the hopper on the assumption that the visit will happen. General rule: daily figure × days away, add the margin, round up. Buying two sizes larger costs more and on many models dispenses less accurately.
How this is calculated
No black box. The calculator runs on four published inputs, all stored in our own database and visible to any editor:
- Daily food intake — a percentage of body weight, stepped by size. Small animals burn more energy per kilogram, so a 4 kg cat and a 40 kg dog do not follow the same rule.
- Daily water intake — millilitres per kilogram of body weight. This is the number that decides your fountain size, and it is the one most buyers get wrong.
- Meals per day — two for most adult dogs, three for cats, who do better with small and frequent meals.
- Safety margins — a 25% buffer on the hopper and a 30% buffer on the fountain, to cover spills, portion drift and evaporation.
What we will not do
We will not tell you that a feeder replaces a person. An automatic feeder keeps the routine going; it does not notice a blockage, a spill or a pet that has stopped eating. Above a certain number of days away, the only responsible answer is a sitter — and the calculator will say so instead of hiding it.
We also will not invent product picks. The result is a specification, not a brand. When our hands-on testing covers a category, you will see the exact model we use and why.