Water Intake Calculator

How much water should you drink each day? The old “8 glasses” advice ignores your size and lifestyle — a 50 kg office worker and a 90 kg athlete do not need the same amount. Enter your weight and activity level to get a personalized daily target in liters, plus how many standard 250 ml glasses that works out to.

How to Use the Water Intake Calculator

1. Enter your body weight in kilograms as measured recently.
2. Choose your activity level — exercise and active jobs raise fluid needs noticeably.
3. Press Calculate to get your daily target in liters.
4. Use the glass count to pace yourself — a glass with each meal plus a few in between usually does it.

Practical example

A 70 kg lightly active person needs about 2.66 liters per day — roughly 11 glasses of 250 ml. An 80 kg athlete needs about 3.64 liters, or 15 glasses. Spreading them across the day (a glass every waking hour or so, plus extra around workouts) makes even the higher target easy to hit without ever feeling waterlogged. Remember that food also contributes: fruits, vegetables, and soups count toward hydration.

Key features and benefits

• Weight-based: scales with your body (33 ml per kg) instead of one-size-fits-all advice.
• Activity-adjusted: adds up to a full extra liter for athletes and heavy training days.
• Glass count: converts an abstract liter figure into an easy daily habit.
• Quick: two inputs, one click, instant answer.
• Private: everything is computed in your browser.

Limitations

This is a general guide for healthy adults. Hot and humid climates, fever, vomiting or diarrhea, intense training, pregnancy, and breastfeeding all raise your needs, while some medical conditions — kidney disease, heart failure, liver disease — require fluid restriction, in which case you must follow your doctor’s limits, not this calculator. As a day-to-day check, thirst and pale-yellow urine are more reliable than any formula. Coffee and tea count toward fluid intake despite their mild diuretic effect, so your morning cup is not working against you the way old myths suggest.