Calculate your daily water intake needs based on body weight, activity level, and climate. Shows litres and glasses, a suggested hourly drinking schedule for the day, and the contribution from food sources.
Enter your body weight in kg or lbs, your activity level, and your climate (temperate, hot, or very hot/humid). Each factor adjusts the base recommendation upward to account for increased fluid loss.
Your recommended daily water intake is shown in litres and equivalent 250 ml glasses. Separate adjustments are shown for exercise and climate so you understand what's driving the recommendation.
A suggested drinking schedule distributes your daily target across waking hours (7am–10pm). Reminders for key moments — morning, pre-meal, and pre-workout — are highlighted.
Evidence-based recommendations: National Academies of Sciences (2004): 3.7 L/day total fluid for men, 2.7 L/day for women (includes water from food, which provides ~20%). After subtracting food water: ~3.0 L (12 cups) for men, ~2.2 L (9 cups) for women as drinks. This calculator uses 35 ml/kg/day as a baseline, adjusted for activity and climate — a widely cited clinical guideline.
Exercise significantly increases fluid loss through sweat. Sweat rates vary from 0.5–2 L/hour depending on intensity, temperature, and individual factors. A general guideline: add 500–750 ml (17–25 oz) per hour of moderate exercise. For high-intensity training or hot conditions, needs can exceed 1 L/hour additional fluid. Weigh yourself before and after exercise — each 1 kg lost equals approximately 1 L of fluid deficit.
The "8×8" rule (eight 8-oz glasses = 1.9 L/day) lacks strong scientific support — it likely originated from a 1945 US Food and Nutrition Board recommendation that was taken out of context. Individual needs vary dramatically based on body size, climate, and activity. The Institute of Medicine recommends listening to thirst as a reliable guide for most healthy adults. Athletes, older adults, and those in hot climates should drink proactively.
All beverages count: water, tea, coffee, milk, juice, and sparkling water all contribute to hydration. Despite the myth, moderate caffeine consumption does not cause net dehydration — a 2014 study found coffee equivalent in hydration to water at typical consumption levels. About 20% of fluid intake comes from food: fruits and vegetables have 80–95% water content; cooked grains and proteins 60–75%.
The most practical indicator is urine colour: Pale yellow (lemonade colour) = well hydrated. Dark yellow = mildly dehydrated — drink more. Amber/orange = significantly dehydrated. Clear = possibly over-hydrated. Other signs of dehydration include dry mouth, headache, fatigue, reduced performance, and dark-coloured urine. Thirst is a reliable indicator for most adults but is less reliable in older adults and during intense exercise.
Hyponatremia (water intoxication) occurs when excess water dilutes blood sodium below safe levels. It is rare but occurs in endurance athletes who drink excessive plain water over several hours without sodium replacement. Symptoms include nausea, headache, confusion, and in severe cases, seizures. During exercise lasting over 1 hour, sports drinks or sodium-containing foods help maintain electrolyte balance alongside adequate hydration.
