Find out exactly how much water you should drink per day based on your weight, activity, and climate.
Calculate Water Needs ↓Based on the standard 35 ml/kg formula adjusted for activity and climate.
Drink 400–500 ml of water first thing in the morning to replenish overnight losses. You lose roughly 300–500 ml of water overnight through breathing and skin evaporation alone, so this simple habit corrects the deficit before your day even starts and helps kick-start digestion.
Drink 500 ml before exercise and 200–300 ml every 15–20 minutes during training. For sessions longer than 60 minutes, or in hot conditions, consider adding electrolytes (sodium, potassium) since sweat carries out more than just water — plain water alone can dilute sodium levels during very long or intense efforts.
Drinking water with meals aids digestion and helps you feel fuller, naturally reducing calorie intake. Research on pre-meal water consumption suggests drinking roughly 500 ml about 30 minutes before eating can modestly reduce the amount of food eaten, particularly for weight management goals.
In hot or humid conditions, increase your intake by 500–1000 ml per day above your baseline. Heat and humidity both raise sweat rate even without exercise, and the effect compounds if you're also physically active outdoors — check your urine colour as a quick guide: pale yellow means you're well hydrated.
This calculator uses the widely cited 35 ml per kilogram of body weight formula as a baseline, then adjusts upward for activity level and climate. For a 75 kg adult at moderate activity in a warm climate, that works out to roughly 2.8–3 litres per day — broadly in line with the general guidance from health authorities like the U.S. National Academies of Sciences, which recommends around 2.7 litres/day for women and 3.7 litres/day for men from all beverages and food combined.
Keep in mind that roughly 20% of daily water intake typically comes from food (especially fruits, vegetables, and soups), so this result already accounts for that in the multiplier. This formula is a general estimate, not a medical prescription: people with kidney disease, heart failure, or those on fluid-restriction medication should follow their doctor's specific guidance rather than a generic calculator. Athletes doing very long endurance events should also account for sweat rate testing rather than relying on a flat formula.