Water Intake Calculator
Estimate how much water to drink daily.
kg or lb
Minutes of exercise per day.
Results update as you type.
This calculator provides estimates based on population research. Results are not medical advice. Consult a qualified healthcare provider before making health or nutrition decisions.
How it works
Water makes up roughly 60 percent of the adult body and drives nearly every physiological process, from regulating temperature and transporting nutrients to cushioning joints and clearing waste through the kidneys. A water intake calculator estimates how much fluid you should take in across a day to replace what you continually lose through urine, breathing, sweat and skin. This tool scales the estimate to body size, using a common guideline of around 33 ml per kilogram of body weight, then adds an allowance for the extra sweat losses that exercise brings. Larger bodies and more active days simply need more fluid, which is why a personalised water intake calculator beats blanket advice like a fixed number of glasses. The U.S. National Academies, which set the Dietary Reference Intakes for water, note that total needs vary widely and that most healthy people meet them by drinking to thirst and eating normally. It is worth remembering that around a fifth of daily water comes from food, and that other beverages count too, so the figure shown here is total fluid, not water you must drink on its own. Athletes, people in hot climates and anyone prone to forgetting to drink use a water intake calculator as a practical daily reminder, adjusting for climate, health and diet.
≈ 33 ml per kg of body weight, plus ~350 ml per 30 min of exercise
The estimate scales with body weight because larger bodies hold more water and lose more through metabolism, skin and breathing, so fluid needs rise roughly in proportion to mass, hence about 33 ml per kilogram. Exercise adds a further allowance, roughly 350 ml per half hour, to replace the water lost as sweat while the body cools itself during sustained activity.
Source:U.S. National Academies (2005), Dietary Reference Intakes for Water
We review all our tools from time to time to ensure accuracy.
Worked example
How to use this calculator
- 1
Enter your values
Enter body weight.
- 2
Adjust the options
Adjust units and exercise if they apply — sensible defaults are already set.
- 3
Read your result
Daily water updates instantly as you type — no button to press.
Frequently asked questions
How much water should I drink a day?
It depends on your size, activity and climate rather than a fixed number. The U.S. National Academies suggest total daily fluid around 3.7 litres for men and 2.7 for women, but that includes water from food and all beverages. This tool personalises the estimate to your weight and exercise. The simplest real-world guide is to drink enough that you rarely feel thirsty and your urine stays pale yellow.
Does coffee, tea or juice count toward hydration?
Yes. Despite the persistent myth, moderate caffeine does not dehydrate you; coffee and tea are still net hydrating, and juice, milk and soft drinks all contribute fluid. Water-rich foods such as fruit, vegetables and soup add a meaningful share too. Plain water remains the best default because it has no calories or sugar, but nearly everything you drink helps you reach your total.
Can you drink too much water?
Rarely, but yes. Drinking a very large volume in a short time can dilute blood sodium, a dangerous condition called hyponatraemia that mainly affects endurance athletes overdrinking during events. For everyday life the risk is minimal if you simply drink to thirst and spread intake through the day rather than forcing large amounts at once. Healthy kidneys comfortably handle normal, steady fluid intake.
How do I know if I am dehydrated?
The clearest everyday signs are thirst, dark yellow urine, infrequent urination, dry mouth, headache and fatigue. Urine colour is the most practical check: pale straw means well hydrated, deep amber means drink more. Thirst is a reliable prompt for most people, though older adults feel it less keenly and should drink proactively. Dizziness or a rapid heartbeat signals more serious dehydration that needs prompt fluids.
Do I need more water when exercising or in hot weather?
Definitely. Sweating during exercise or in heat can cost half a litre to over a litre of fluid per hour, which must be replaced to maintain performance and safe body temperature. This tool adds roughly 350 ml per half hour of exercise for that reason. In hot or humid conditions, or at altitude, raise your intake further and drink before you feel thirsty, since thirst lags behind actual loss.