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Water Intake Calculator
Calculate your recommended daily water intake based on your weight, activity level, and climate. Get your target in ml, oz, and glasses, plus an hourly drinking schedule.
Activity level
Climate
How to use the Water Intake Calculator
Enter your weight
Type your body weight and select kilograms or pounds. Your weight is the primary factor in determining your base hydration needs.
Select your activity level
Choose from Sedentary (desk job, little exercise) up to Very Active (twice-daily training). Exercise increases fluid loss through sweat and breathing.
Choose your climate
Hot or humid environments significantly increase water loss. Select Cool (air-conditioned), Temperate, or Hot/Humid to account for your environment.
Read your daily target
See your total daily water intake in litres, oz, and glasses. Scroll down for a breakdown of each contributing factor and an hourly drinking schedule from 7am to 10pm.
About this Water Intake Calculator
Water is essential for virtually every bodily function: regulating temperature, transporting nutrients, lubricating joints, flushing waste, and enabling chemical reactions at the cellular level. Despite this, mild dehydration is surprisingly common — studies suggest that many people operate slightly below optimal hydration without realising it, experiencing reduced concentration, energy, and mood as a result. The popular '8 glasses a day' rule (about 2 litres) is a useful starting point but doesn't account for individual variation. Body size matters significantly: a 100kg person needs considerably more water than a 50kg person. Activity multiplies requirements — you can lose 0.5–1 litre per hour of moderate exercise, more in heat. Climate matters too: in hot and humid conditions, your body works harder to regulate temperature and sweat rate increases substantially. Our calculator uses a weight-based formula (33ml per kg of body weight) as the baseline, then adds activity-based increases and climate adjustments. This approach is consistent with recommendations from sports nutrition researchers and reflects current understanding of hydration needs across different lifestyles. The hourly schedule is a practical tool for spreading water intake throughout the day. Research shows the body absorbs water more efficiently in small, frequent amounts rather than large infrequent gulps. Drinking little and often also helps maintain consistent energy levels and reduces the fatigue that often accompanies mild dehydration in the afternoon.
Frequently Asked Questions
General guidelines suggest 2–3.7 litres per day for adults, but your individual needs depend on weight, activity level, climate, and diet. The commonly cited '8 glasses a day' (about 2 litres) is a reasonable baseline for sedentary adults in a temperate climate.
Yes, significantly. You lose around 0.5–1 litre of water per hour of moderate exercise through sweat and respiration. Our calculator adds extra water intake for active days and hot climates to account for increased losses.
Yes, mostly. Despite caffeine's mild diuretic effect, research shows that tea and coffee still contribute positively to total fluid intake. The net hydration effect is positive for normal consumption (1–4 cups per day). Pure water is always the best choice, but other drinks count.
Early signs include dark yellow urine, dry mouth, headache, fatigue, and reduced concentration. Severe dehydration causes dizziness, rapid heartbeat, and confusion. A simple test is urine colour — pale straw yellow indicates good hydration; dark amber suggests you need to drink more.