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Daily Water Intake Calculator

Find out how much water you should drink per day based on your weight, physical activity level and climate.

Water is essential for almost every process in the body: it regulates body temperature, transports nutrients, aids digestion and removes metabolic waste. However, hydration needs are not the same for everyone — they vary depending on body weight, the intensity of physical activity and climatic conditions.

This calculator applies the formula used by dietitians and nutritionists: a base factor of 30 to 40 ml per kilogram of body weight, adjusted for your activity level, plus an extra 500 ml in hot climates to compensate for fluid lost through sweating. The result tells you how many litres of fluid you should drink throughout the day to stay properly hydrated.

Your data

Recommended daily water intake

2.3 L

Equivalent to 9 glasses of water (250 ml each)

WHO minimum recommendation: 1.5 litres/day for adults.

Results are indicative only. Hydration needs may vary for health reasons. Consult a healthcare professional if you have any concerns.

How your water needs are calculated

The starting point is your body weight, because fluid needs are proportional to the mass that has to stay hydrated. The formula multiplies your weight by a factor in millilitres per kilogram that rises with physical activity: 30 ml/kg if you are sedentary and up to 40 ml/kg if you train intensely almost every day. An extra 500 ml is added when you live or train in a hot climate, to compensate for the water you lose through sweat.

Worked example

A 70 kg person who is lightly active (factor 33 ml/kg) in a temperate climate would need 70 × 33 = 2,310 ml, or about 2.3 litres a day — the equivalent of just over 9 glasses of 250 ml. If that same person lived in a hot climate, they would add 500 ml and reach around 2.8 litres per day.

Millilitres per kilo by activity level

Activity levelml per kgExample (70 kg)
Sedentary30 ml/kg2.1 L
Light33 ml/kg2.3 L
Moderate36 ml/kg2.5 L
Intense40 ml/kg2.8 L

How to interpret the result

The figure you get is a daily guide, not a strict hour-by-hour obligation. The best approach is to spread it out by drinking steadily throughout the day rather than large amounts at once, and to use urine colour as a practical indicator: pale yellow means good hydration, while a dark shade means you should drink more. On very hot days, during prolonged exercise, or with fever, diarrhoea or vomiting, your needs rise and it is wise to drink above the calculated figure.

Frequently asked questions

The most widely used formula among dietitians and nutritionists starts with a base factor of 30-40 ml per kilogram of body weight, adjusted for physical activity level. An extra 300-700 ml is added in hot climates to compensate for sweat losses. This calculator uses 30 ml/kg for sedentary people up to 40 ml/kg for high-intensity athletes, plus an additional 500 ml in hot climates.

Yes. Approximately 20-30% of daily fluid intake comes from solid foods, especially fruits and vegetables (watermelon, cucumber and lettuce contain over 90% water). However, the values in this calculator refer exclusively to fluids you should drink, as this is the easiest way to monitor hydration. If your diet is rich in fruit and vegetables, you may sit at the lower end of the range.

The first signs of mild dehydration are thirst, dark yellow urine, fatigue and difficulty concentrating. A dehydration of just 2% of body weight already leads to a measurable reduction in physical and cognitive performance. Severe dehydration (>5%) can cause dizziness, rapid heartbeat and confusion, and requires medical attention. As a practical rule, your urine should be pale yellow; if it is clear you are well hydrated, if it is dark you need to drink more.

Yes, although it is uncommon. Drinking excessive amounts of water in a very short time can cause hyponatremia, a dangerous dilution of blood sodium that leads to headache, nausea, confusion and, in severe cases, seizures. It usually happens in endurance athletes who overdrink or in rapid-intake challenges. In a healthy person, the kidneys easily clear surplus fluid spread across the day; the risk only appears with very large volumes taken all at once. That is why the recommendation is to drink regularly and moderately rather than forcing a specific figure in one go.

Yes. For years caffeinated drinks were thought to be dehydrating, but current evidence shows that coffee and tea drunk in moderation hydrate almost as much as water: their mild diuretic effect is offset by the volume of fluid they provide. The same applies to herbal teas, milk and the water contained in fruit and vegetables. What you should limit is sugary drinks and alcohol: alcohol does have a real dehydrating effect, because it suppresses the antidiuretic hormone and increases urine production.

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