Estimate how much water you need each day from your weight, exercise and climate.
kg
lb
min
Enter the values to see the result here.
For general information, not medical advice. Talk to a doctor before making health decisions.
Formula
The estimate adds three parts, in millilitres:
V=35w+350⋅30t+c
where w is body weight in kg, t is daily exercise in minutes and c is 500 for a hot or humid climate (0 otherwise). Cups divide the total by 250 ml. This is a general guide, not a clinical prescription.
Worked example
A person weighing 70 kg, exercising 60 minutes a day in a hot climate.
Base: 35×70=2,450 ml.
Exercise: 350×60/30=700 ml.
Climate: 500 ml.
Total: 2,450+700+500=3,650 ml, or 3.65 L, which is 14.6 cups of 250 ml.
Common mistakes
Treating the total as plain water only. Food and other drinks supply part of it.
Ignoring heat: a day outdoors in summer can add well over a litre.
Drinking it all at once instead of spacing it through the day.
Applying the adult formula to children, pregnant or breastfeeding women, or people on fluid restrictions.
Frequently asked questions
Do I really need eight glasses a day?
The eight-glasses rule is a round number, not a measured need. Weight, activity and heat change it a lot. A 50 kg person at rest needs around 1.75 L in total; an 85 kg person who trains needs closer to 3.5 L.
Does tea, coffee or food count?
Yes. Roughly 20% of daily water comes from food, and tea and coffee count in moderation. Plain water is still the best default because it carries no sugar or caffeine.
How should I drink during Ramadan?
The total need stays similar, but it has to fit between iftar and suhoor. Spread it out: two to three glasses at iftar, one every hour or so in the evening, and two at suhoor. Check with a doctor if you take medication or have a medical condition.
Can I drink too much water?
Yes, though it is rare. Drinking several litres in a very short time can dilute blood sodium (hyponatraemia). Sip steadily and drink to thirst alongside this estimate.