Water Intake Calculator

How much water should I drink a day? This calculator turns the vague advice into a concrete number built from three things that actually change your needs: body weight, daily exercise and climate. The baseline is roughly 35 milliliters per kilogram of body weight — the mid-range of common dietetic guidance — so a 70 kg person starts at about 2.45 liters. On top of that, every 30 minutes of exercise adds about 350 ml to replace what you sweat out, and living in a hot or humid climate adds another 500 ml.

The answer comes in three practical units at once: liters for the big picture, milliliters for precision, and 250 ml glasses for the habit you can actually track through the day. The calculator also shows the full breakdown — base amount, exercise addition and climate bump — so you can see exactly how your target was built rather than trusting a black box. Popular one-size-fits-all rules like 'eight glasses a day' ignore the difference between a 50 kg office worker in a temperate city and a 100 kg runner in the tropics; a weight-based estimate scales with the person.

Everything runs locally in your browser: your weight and activity data are never uploaded, stored or shared, and no registration stands between you and the result. Enter three values, press the button, and copy the summary as plain text if you want to keep it in your notes or fitness journal.

Be honest about what this number is: an estimate of total fluid needs, not a medical prescription. Roughly 20 percent of your fluid typically comes from food, coffee and tea count toward the total, and thirst remains a good everyday signal. Needs also shift with pregnancy, breastfeeding, illness, certain medications and conditions like kidney or heart disease — in those cases, ask a doctor instead of a calculator.