Pet Daily Water Needs Calculator
Daily water for a dog or cat in ounces or ml from weight, activity and climate, plus diet and life stage for dogs, with a 7-day drinking log for dogs. How it works
Use the Pet Daily Water Needs Calculator
About the Pet Daily Water Needs Calculator
Osborne (2003) puts a dog’s daily water at 140 × weight in kg^0.75 ml and a cat’s at 80 × kg^0.75: a 20 lb (9.07 kg) dog gets 140 × 9.07^0.75 = 732 ml and a 4 kg cat 80 × 4^0.75 = 226 ml, which is 7.7 oz. The calculator then applies its own factors. With the default standard bowl, which it counts as 0.95, a moderately active adult dog on dry kibble shows 23.5 oz (695 ml), within 21.2 to 25.9 oz; the gravity dispenser (1.0) leaves the 732 ml unchanged.
Base maintenance water by body weight (Osborne 2003), before any adjustment
| Body weight | Dog: 140 × kg^0.75 | Cat: 80 × kg^0.75 |
|---|---|---|
| 2 kg (4 lb) | 235 ml (8.0 oz) | 135 ml (4.5 oz) |
| 4 kg (9 lb) | 396 ml (13.4 oz) | 226 ml (7.7 oz) |
| 5 kg (11 lb) | 468 ml (15.8 oz) | 267 ml (9.0 oz) |
| 10 kg (22 lb) | 787 ml (26.6 oz) | 450 ml (15.2 oz) |
| 20 kg (44 lb) | 1324 ml (44.8 oz) | 757 ml (25.6 oz) |
| 30 kg (66 lb) | 1795 ml (60.7 oz) | 1025 ml (34.7 oz) |
| 40 kg (88 lb) | 2227 ml (75.3 oz) | 1272 ml (43.0 oz) |
Ounces are US fluid ounces, 29.5735 mL each. The tool multiplies the base by its own adjustment factors, so its estimate for a given pet differs from these figures.
A 20 lb adult dog by diet (moderate activity, normal climate, standard bowl)
| Diet | Multiplier with the 0.95 bowl factor | Daily water | Range (±10%) |
|---|---|---|---|
| Dry kibble | 0.95 | 695 ml (23.5 oz) | 21.2 to 25.9 oz |
| Wet or canned | 0.6175 | 452 ml (15.3 oz) | 13.8 to 16.8 oz |
| Mixed | 0.8075 | 591 ml (20.0 oz) | 18.0 to 22.0 oz |
| Raw | 0.7125 | 521 ml (17.6 oz) | 15.9 to 19.4 oz |
| Home-cooked | 0.855 | 626 ml (21.2 oz) | 19.0 to 23.3 oz |
The diet multipliers, the bowl factor and the ±10% band are this tool’s own, not from a cited source.
Methodology
Base water = 140 × weight in kg^0.75 ml for a dog and 80 × weight in kg^0.75 ml for a cat (Osborne, dvm360, 2003). The tool multiplies by its own factors for activity and climate, and for a dog also life stage, diet, bowl and outdoor heat. The range is the estimate times 0.9 to 1.1. The 140 and 80 coefficients, the exponent and the 90 and 45 ml per kg limits are Osborne’s; every other factor and the range are the tool’s own.
How to use this tool
- Choose Dog or Cat and enter the weight in pounds or kilograms. A weight above 0 and up to 300 lb (136.1 kg) is accepted.
- Set activity and climate. For a dog, also set life stage, diet, water bowl, indoor or outdoor and meals per day.
- Read the daily estimate and its range, in ounces, milliliters, cups or liters.
Frequently asked questions
- How much water should a dog drink a day?
- Osborne (2003) gives maintenance water for dogs as 140 × body weight in kg^0.75 ml. For a 10 kg dog that is 787 ml, or 26.6 oz, before this tool’s adjustments. Smaller dogs need more per kg: 118 ml per kg at 2 kg against 56 ml per kg at 40 kg.
- How much water should a cat drink a day?
- The same article gives 80 × body weight in kg^0.75 ml for cats. A 4 kg cat has a base of 226 ml, or 7.7 oz, and a 5 kg cat has 267 ml, or 9.0 oz. The tool changes the base for activity and climate for cats.
- Why is body weight raised to the power 0.75?
- Water need rises more slowly than weight. A pet twice as heavy needs about 1.68 times as much water, not 2 times, because 2^0.75 is 1.68. The Merck Veterinary Manual uses the same exponent with 132 for dogs and 80 for cats, as a maintenance fluid figure for clinics rather than a drinking target for owners. This tool uses Osborne’s 140, which gives a dog about 6% more than Merck’s 132.
- When is a pet drinking too much?
- Above about 90 ml per kg a day for a dog or 45 ml per kg for a cat. Osborne gives those as the upper limit of normal and calls intake above them evidence of polydipsia, which has several causes, so call your veterinarian. For a 20 lb dog, 90 ml per kg is about 816 ml, or 27.6 oz.
- When does the vet alert in the drinking log appear?
- For dogs only, after at least 3 logged days in the last 7 whose average is above 90 ml per kg and also above the top of the range the tool estimates for that dog. The second test is there because the limit and the formula do not line up for small pets: the estimate itself is above 90 ml per kg for a dog under about 4.8 kg, and above 45 ml per kg for every cat under about 10 kg (a 4 kg cat is estimated at 57 ml per kg), which is why cats get no alert. The tool does not diagnose.
- What are the signs of dehydration in a dog, and how do I get it to drink more?
- Dry or tacky gums, skin on the shoulders that is slow to fall back after you lift it, sunken eyes, tiredness or weakness, and eating less. PetMD lists these among the signs and advises taking a dog that shows them to a veterinarian; a puppy that is both vomiting and has diarrhea can dehydrate quickly. To help a healthy dog drink more, add water to its kibble, try a fountain, put out more than one bowl and offer water after exercise.
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