💧Daily Water Intake Calculator

How much water to drink per day — how does the calculator work?

Our water intake calculator determines your daily fluid needs based on two key parameters: body weight and physical activity level. The base is 35 ml per kilogram of body weight — a value recommended by most dietetic organisations. An activity surplus is then added: approximately 350–500 ml for every 30 minutes of exercise. The result is displayed in real time — in litres and in glasses (250 ml each) — together with a breakdown of the base and the activity add-on.

Why is hydration so important?

Water makes up about 60% of an adult's body weight and is involved in virtually every metabolic process: from temperature regulation, through nutrient transport, to toxin removal. Even 1–2% dehydration reduces concentration and physical performance, and at 5% headaches and fatigue may appear. Regularly checking your requirements — especially in summer or during intense training — helps maintain a proper fluid balance without waiting for thirst, which is often a delayed signal.

Frequently asked questions

How much water should I drink per day?

A common rule of thumb is about 35 ml per kilogram of body weight. A person weighing 70 kg should drink around 2.5 litres per day — before accounting for physical activity. Regular exercise increases the requirement by 350–500 ml for every 30 minutes of effort.

Do coffee and tea count towards hydration?

Yes, beverages such as tea and coffee contain water and partially hydrate the body, although caffeine has a mild diuretic effect. Water intake calculators generally refer to plain water or drinks with minimal caffeine content.

Why do I need more water on hot days?

In high temperatures the body loses more fluid through sweating. It is estimated that on a hot day the requirement increases by around 500 ml or more. Our calculator includes an optional hot-day adjustment.

Is the calculator result medically binding?

No. The result is indicative and based on widely used estimation formulas. Actual requirements depend on health status, diet, climate, medication, and many other factors. If in doubt, consult a doctor or dietitian.