Water Intake Calculator
Get your personalized daily water intake recommendation based on your body weight, activity level, and climate.
How much water do you really need?
The common advice of "8 glasses a day" is a rough guideline, not a universal prescription. Your actual needs depend on your body size, how active you are, where you live, and other factors like diet and health conditions.
The formula used
This calculator starts with a base of 35 ml per kg of body weight, then adds estimated losses from physical activity and heat exposure. This approach is consistent with recommendations from the European Food Safety Authority (EFSA).
Why body weight matters for hydration
Larger bodies contain more total water and generate more metabolic heat during activity, requiring more fluid to maintain balance. A 90 kg person doing the same workout as a 60 kg person will lose significantly more fluid through sweat and respiration — their baseline needs are higher before accounting for any additional activity.
Exercise and heat significantly increase needs
Sweat rates during moderate exercise typically range from 0.5 to 1.5 litres per hour depending on intensity, temperature, and individual variation. In hot or humid conditions, this can exceed 2 litres per hour. Dehydration of just 1–2% of body weight can reduce aerobic performance by 5–10% and impair cognitive function. Most people don't notice thirst until dehydration has already begun, which is why proactive hydration is recommended during prolonged exercise.
What counts toward your daily fluid intake?
All fluids count — not just plain water. Tea, coffee, milk, juice, and water-rich foods all contribute. About 20% of daily water intake typically comes from food. Coffee and tea, despite containing caffeine, still provide a net hydration benefit at normal consumption levels (2–4 cups/day). The idea that coffee dehydrates you is largely a myth.
Signs you're drinking enough
Urine colour is the most practical hydration indicator. Pale straw yellow means good hydration. Dark yellow or amber signals dehydration. Completely clear urine can indicate overhydration. Other signs of adequate hydration include regular urination (approximately every 2–4 hours), moist lips, and consistent energy levels throughout the day.
Tips to hit your daily target
- Keep a marked water bottle visible — out of sight, out of mind applies to hydration too.
- Drink a glass before each meal. It improves hydration and supports portion control.
- Eat water-rich foods: cucumber, watermelon, celery, strawberries, and soups all contribute significantly.
- Increase intake proactively before outdoor activity in warm weather — don't wait until you're thirsty.
- After alcohol, drink at least one glass of water per alcoholic drink consumed, as alcohol accelerates fluid loss.