Calculate how much water you should drink per day online free - no signup. Based on your weight, activity level, and climate, get a personalized daily hydration recommendation.
Dehydration causes headaches, fatigue, and poor focus before you even feel thirsty - especially during workouts. A target that accounts for your actual body size is more useful than a generic rule that was never based on science in the first place.
The '8 glasses a day' rule ignores your weight, activity level, and climate. Enter your details and get a personalized daily water target - in millilitres and glasses - based on your body weight.
Set a daily water goal when tracking hydration for fitness or health, calculate how much water to drink on high-activity days, understand how body weight affects hydration needs, estimate water intake targets for weight loss plans, track daily hydration progress with a concrete ml target, and compare intake across different activity levels.
The most common question is whether coffee, juice, or other beverages count. The short answer: yes, most beverages contribute to hydration - though plain water remains the most efficient source.
Input your body weight in kg or lbs.
Select your daily exercise level.
Select your climate type (hot, moderate, cold).
See your recommended daily water intake in ml, liters, and cups.
Common questions about this tool and how to use it.
A common baseline is 35ml per kg of body weight. A 70kg adult needs approximately 2,450ml (2.45L or about 8 glasses) per day. This increases with exercise, hot weather, high-altitude environments, illness, or if you consume diuretics like caffeine. The '8 glasses a day' rule was never based on scientific evidence - your actual need depends on your body size and activity level.
Yes - caffeinated beverages like coffee and tea still contribute to hydration despite being mild diuretics. The diuretic effect of caffeine is weaker than the hydrating effect of the water in the beverage. Studies show that moderate coffee consumption (3–4 cups/day) has a net neutral to positive effect on hydration. Sugary drinks count too, but add empty calories.
The most reliable indicator is urine color. Pale yellow (like lemonade) indicates good hydration. Dark yellow or amber indicates dehydration. Clear urine may indicate over-hydration. Other signs of dehydration include headache, fatigue, dry mouth, dizziness, and reduced concentration - often appearing before you feel thirsty.
Yes. During moderate exercise, add approximately 500ml (17 oz) per hour of activity. For intense exercise in hot conditions, you may need 750–1,000ml per hour. A practical approach: weigh yourself before and after exercise - every 1 kg of weight lost represents approximately 1L of fluid that should be replaced.
Yes - this is called hyponatremia (water intoxication). It occurs when drinking large amounts of plain water dilutes sodium levels in the blood. It is rare in everyday life but can occur during endurance events where athletes drink water without replacing electrolytes. For most people, the kidneys can excrete excess water safely up to about 1L per hour.
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