How much water should you drink each day? Get a personalised estimate based on your weight, climate and how much you sweat.
Educational use only. This calculator is a general-purpose tool and does not replace medical advice. If a result surprises you or you have an underlying condition, consult a clinician before acting on it.
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The familiar "eight glasses a day" advice is useful as a starting point but ignores body size, activity, climate and what else you are drinking. Larger people, hot-climate residents and anyone who trains regularly need more. Smaller, sedentary people in cool climates need less.
A common starting estimate used by sports dieticians is 30–35 ml per kilogram of body weight per day, plus an extra 300–500 ml per 30 minutes of moderate exercise. This calculator uses that baseline, adjusts for climate, and produces a daily target in litres, fluid ounces and standard cups.
Remember that water comes from food too — fruits, vegetables, soups and even bread contain 20–80% water. The number on screen is total fluid, not "extra" fluid on top of food. Most people in temperate climates meet 70% of their needs from drinks and 30% from food.
Yes, but it is rare. Drinking many litres in a short time can dilute sodium dangerously (hyponatremia). Spread intake across the day rather than slamming a litre at once.
Yes. Modern research has overturned the old "they dehydrate you" claim. The water content in the drink more than offsets the mild diuretic effect of the caffeine.
Thirst lags behind dehydration, especially as we age. Drinking proactively prevents the headaches, fatigue and concentration drops that come with mild dehydration.
It is not wrong, just imprecise. For an average adult it lands close to the right answer. Bigger or more active people need more; smaller or sedentary people may need less.
The Water Intake Calculator lives alongside BMI Calculator, Body Fat Percentage Calculator, Ideal Weight Calculator on the Health & Fitness page. That landing page collects every health & fitness tool Dailiyo publishes, plus the editorial notes on formula sources, review cadence and how each result should (and should not) be interpreted. If a related health & fitness calculation isn't yet in the collection and you'd like to see it, drop a line via the contact page — the editorial team reviews every request and prioritises tools that come up most often in reader questions.