Daily Water Intake Calculator

The recommended amount for adults is about 35 ml per kilogram of body weight, which equals about 2.45–2.7 litres for a 70 kg person. This increases with physical activity and in hot weather. Women typically need about 2.0–2.2 l and men about 2.5–3.0 l per day.

Water requirements are directly proportional to body mass — the 35 ml/kg rule is a widely used guideline. Heavier people have greater blood volume and tissue mass requiring hydration, so they need more fluids.

Yes — during exercise we lose water through sweat and breathing. Lightly active people need about 250 ml more, active people about 500 ml, and very active people (intense daily training) about 750 ml above the baseline. During prolonged exercise replenish fluids every 15–20 minutes.

In hot weather the body loses significantly more water through sweating — up to 500 ml or more above normal requirements. At temperatures above 30°C it is advisable to drink at least 500 ml extra and avoid direct sun during peak hours.

Assuming a standard 250 ml glass, a 70 kg lightly active person at normal temperature needs about 10–11 glasses per day. The calculator gives an individual result based on your weight, activity and temperature.

Yes — contrary to popular belief, coffee and tea do hydrate the body, though less efficiently than plain water. Caffeine has a mild diuretic effect but the net hydration benefit is positive. Most of your daily target should still come from still or low-sodium water.

Even at 1–2% water loss you may experience headaches, fatigue and difficulty concentrating. At 5% physical and mental performance drops. Signs include dark urine, dry mouth, dizziness and thirst. Thirst is already a sign of mild dehydration — drink regularly rather than waiting.

Yes — hyponatraemia (water intoxication) occurs when excessive water dilutes blood sodium. It mainly affects athletes drinking excessively during long events. Healthy kidneys can process about 0.8–1 litre per hour, so the risk is low with normal drinking habits.

Yes — children have higher water needs relative to body mass (about 50–60 ml/kg for infants). Older children (6–13 years) need about 1.6–2.1 l per day and teenagers approach adult norms. This calculator is designed for adults (minimum 20 kg).

The simplest indicator is urine colour: pale straw or light yellow means good hydration; dark yellow or orange means you need more fluids. You can also check skin turgor (pinch the back of your hand) — well-hydrated skin snaps back immediately.