Water Intake Calculator
How much water to drink daily from your weight and activity.
Formula
About this calculator
Staying properly hydrated affects everything from energy and concentration to athletic performance and digestion, yet most people rely on vague rules of thumb. A water intake calculator gives you a personalised daily target based on the two factors that matter most: your body weight and how much you exercise.
The baseline uses the common guideline of roughly 35 milliliters of water per kilogram of body weight — so a heavier body, which contains more water and burns more energy, gets a proportionally higher target. On top of that, the calculator adds about 350 milliliters (12 ounces) for every 30 minutes of exercise to replace what you lose through sweat and faster breathing.
The result is shown three ways — liters, standard cups and fluid ounces — so it fits whatever units you think in. This makes it easy to translate into a practical plan, such as a number of bottles or glasses to spread across the day rather than gulping large amounts at once.
Individual needs vary more than any formula can capture. Hot or humid weather, high altitude, illness with fever, pregnancy and breastfeeding all raise requirements, while some of your daily fluid also comes from food and other drinks. Use this figure as a sensible starting target and let thirst and urine color — pale yellow is the goal — fine-tune it.
Frequently asked questions
How much water should I drink a day?
This tool estimates roughly 35 mL per kg of body weight, plus about 350 mL for every 30 minutes of exercise. It personalises the old 8-glasses rule to your size and activity.
Does other liquid and food count?
Yes. Tea, coffee, milk and water-rich foods all contribute to your total fluid intake, so you don't need to hit the entire figure from plain water alone.
When do I need more water?
In hot or humid weather, at altitude, during illness with fever, and when pregnant or breastfeeding. Increase your intake above the baseline in these situations.
Can I drink too much water?
Rarely, but excessive intake over a short time can dilute blood sodium (hyponatremia). Spread water through the day and let thirst guide you rather than forcing large volumes.
Related calculators
⚠️ Hydration estimates are general guidance, not medical advice. Needs vary with climate, health and activity; consult a doctor for medical conditions affecting fluid intake.