Free Online Water Intake Calculator

1. Pick metric or imperial and enter your weight.
2. Select your activity level and climate.
3. Read the recommended daily intake in litres, ounces and 250 ml glasses.

There's no universal "correct" amount of water to drink, but a useful rule of thumb is 33 ml per kg of body weight as the maintenance baseline, with extra to cover exercise sweat and hot or humid weather. That works out to about 2.3 L for a 70 kg adult before any activity adjustment — close to the often-quoted 8 glasses a day.

This tool starts from that 33 ml/kg baseline, adds 350 ml for moderate exercise or 700 ml for an hour or more of training and adds 250–500 ml for warm or hot climates. Output is shown in litres, US fluid ounces and 250 ml glasses so you can track in whichever unit suits you. Athletes calibrating training-day intake, office workers in dry air-conditioned buildings and parents teaching kids hydration habits all use targets like these.

Caffeinated drinks count toward hydration in moderation; alcohol does not. Real needs vary with health conditions, pregnancy, medication, kidney function and salt intake — this is informational only, not medical advice. People with heart or kidney conditions should follow their clinician's targets rather than a generic formula.