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Hydration

Water Intake Calculator (Daily Hydration)

Calculate how much water you should drink each day based on your body weight, activity level, and climate.

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Water Intake Calculator
Calculate your daily water requirement based on weight, activity and climate
Enter your details to calculate water intake

Medical disclaimer. This calculator is provided for educational and informational purposes only and does not constitute medical advice, diagnosis, or treatment. Always consult a qualified healthcare professional regarding your health, diet, exercise, or medication decisions. Read full disclaimer →

About Water Intake Calculator

Adequate hydration is essential for metabolism, kidney function, joint lubrication, and cognitive performance. The standard recommendation of 8 glasses (2 litres) per day is a rough guideline; actual needs vary significantly by body weight, activity level, climate, and diet. A common formula: Daily water (litres) = Body weight (kg) 0.033. Add 350-500 ml for every 30 minutes of moderate exercise.

Signs of mild dehydration include dark urine, fatigue, headaches, and difficulty concentrating these appear before you feel thirsty. About 20% of daily water intake comes from food (fruits, vegetables, soups). In hot climates or during intense exercise, electrolyte replacement (sodium, potassium) is as important as water volume to prevent hyponatraemia. The best hydration test: urine should be pale yellow. Use this calculator to set a personalised daily hydration target.

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Frequently Asked Questions

This calculator uses the common formula of 35 ml of water per kilogram of body weight as a baseline (roughly 2.45 litres for a 70 kg adult). It then adds extra water for your activity level (up to +0.9 L for athletes/hard training) and for hot or humid climates (up to +0.8 L), since sweat losses increase fluid needs.
The '8 glasses a day' guideline is a reasonable starting point but is not personalised. Since needs vary by body weight, activity, and climate, a 90 kg athlete training in a hot climate needs considerably more than a sedentary 55 kg person in an air-conditioned office. This calculator adjusts the baseline for those three factors to give a more tailored estimate.
The most practical day-to-day indicator is urine colour: pale yellow generally indicates adequate hydration, while dark yellow urine, fatigue, headaches, or difficulty concentrating can be early signs of mild dehydration, often appearing before you feel thirsty. Track your intake against your calculated target and adjust based on these signals.
Yes. Roughly 20% of daily water intake typically comes from food, especially water-rich foods like fruits, vegetables, and soups. The litre target from this calculator is meant to represent total fluid intake from drinks; if you eat a lot of water-rich foods you may need slightly less from beverages alone.
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