What this calculator does
The Pet Daily Water Intake Calculator estimates how much water a dog or cat needs each day, expressed in milliliters (mL/day), based on the animal's species and body weight in kilograms. It gives a quick reference figure to help owners judge whether their pet is drinking a sensible amount.
How to use it
Choose your pet's species (Dog or Cat), then enter its body weight in kilograms. If you only have a weight in grams, divide by 1000 first (for example 4500 g = 4.5 kg). The result is the estimated daily water requirement, rounded to the nearest 10 mL, and it already includes water obtained from food.
The formula explained
A healthy pet's daily water need in milliliters is approximately equal to its daily energy requirement in kilocalories. Energy needs scale with body weight to the three-quarter power (metabolic scaling): \(\text{RER} = 70 \times W^{0.75}\). Applying species-specific life-stage factors gives the working formula used here:
Dog: $$\text{Water (mL)} = 112 \times W^{0.75}$$Cat: $$\text{Water (mL)} = 84 \times W^{0.75}$$
where \(W\) is body weight in kilograms. The coefficients 112 and 84 reproduce the reference table published by a pet-food guide (originating from Japan's Ministry of the Environment), and the result is rounded to the nearest 10 mL.
Worked example
For a 10 kg dog: \(10^{0.75} = 5.6234\), so $$112 \times 5.6234 = 629.8$$ rounded to 630 mL/day. For a 5 kg cat: \(5^{0.75} = 3.3437\), so $$84 \times 3.3437 = 280.9$$ rounded to 280 mL/day.
FAQ
Does this include water from food? Yes. The figure represents total water intake, including moisture in wet or dry food, so cats fed canned diets may drink less from the bowl.
Is more or less than this a problem? It is only a guideline. Hot weather, exercise, illness, pregnancy, and lactation all raise needs. Sudden large changes in drinking can signal a health issue worth a vet visit.
Why are the dog and cat numbers different? Cats have lower maintenance energy requirements per kilogram than active dogs, so the species coefficient (84 vs 112) is smaller.
