Water makes up about 60% of your body and is involved in nearly every physiological process — regulating temperature, flushing out waste, transporting nutrients, and lubricating joints. When you are low on fluids, fatigue, headaches, poor concentration, and constipation become more likely; staying steadily hydrated, on the other hand, supports your metabolism and skin health. But the old advice of "eight glasses a day" is a generalization that ignores your weight and activity level. This calculator uses your own weight and activity to give a more personalized daily target in mL, liters, and the number of 200 mL cups.
The calculation uses the widely cited guideline of 30–35 mL per kg of body weight. A sedentary, low-activity lifestyle is figured at about 30 mL per kg, light exercise at 33 mL per kg plus an adjustment, and heavy exercise or lots of sweating at 35 mL per kg plus a larger adjustment. For example, a person weighing 65 kg with low activity is recommended about 1.95 L, while a very active person is recommended about 2.9 L. Since some water also comes from food, soup, and fruit, you can aim for roughly 70–80% of the recommended amount as plain drinking water. The weight you enter is never sent to a server — everything is calculated inside your browser.
How to Use
- 1
Enter your weight
Enter your body weight in kilograms. The recommended intake scales with weight.
- 2
Pick an activity level
Choose the level closest to your usual day among low, moderate, and high. The more you exercise or sweat, the more water you need.
- 3
Check the result
Your recommended daily intake is shown in liters and mL, plus the number of cups (based on a 200 mL cup).
- 4
Copy the result
Use the copy button to save your target intake and use it for a daily check-in.
When It's Useful
Set a daily water goal
Instead of a vague "eight glasses," set a concrete liter and cup goal that matches your weight and activity.
Convert to your bottle size
Since the target is shown in 200 mL cups, it is easy to work out how many times you need to refill the bottle you carry.
Plan hydration before exercise or hiking
On a day with heavy sweating, choose "high" to plan ahead for your increased water needs.
Check for an under-hydration habit
If your usual intake falls well short of the recommendation, this is a good prompt to consciously drink more.
Tips
- Sipping water every 2–3 hours is gentler on absorption and your kidneys than drinking it all at once.
- A glass of water right after waking up replaces fluids lost overnight and helps get your gut moving.
- Caffeinated drinks like coffee and green tea have a diuretic effect, so they do not fully count toward your plain water intake.
- Dark yellow urine is a sign of under-hydration, while pale yellow indicates a good fluid balance.
- Because you also get water from food, soup, and fruit, aiming for about 70–80% of the target as plain drinking water is enough.
- On days with heavy sweating or hot weather, water alone may not be enough. Electrolytes are lost too, so top up with salty food or a sports drink.
FAQ
How is the recommended daily water intake calculated?
It is based on roughly 30–35 mL per kg of body weight depending on activity. This calculator applies 30 mL for low activity, 33 mL plus an adjustment for moderate, and 35 mL plus an adjustment for high activity.
How much do the activity levels differ?
For a 65 kg person, for example, low activity is about 1.95 L, moderate about 2.4 L, and high about 2.9 L — the more active you are, the higher the recommendation.
Does it have to be plain water?
No. Water in food such as soup, fruit, and vegetables contributes too. However, caffeinated and alcoholic drinks have a diuretic effect and do not fully count as pure hydration.
Is it okay to drink too much water?
Drinking excessively in a short time carries a risk of hyponatremia (low blood sodium). It is safer to spread the recommended amount across the day.
How much more should I drink when exercising?
You need to replace the fluids lost through sweat, so choose the "high" activity level. During intense exercise, it is best to add extra water before, during, and after.
Can I follow this recommendation if I have kidney or heart conditions?
No. If you have kidney or heart conditions, or are pregnant or breastfeeding, your ideal intake can be very different, so be sure to consult a healthcare professional. This calculator is for reference only and assumes a healthy general adult.
Is my information stored?
No. Your weight and activity level are used only for the calculation inside your browser and are never sent to a server.