Water Intake Calculator
Enter your body weight and how many minutes you exercise (or spend in heat) today to get a personalized daily water intake target in liters, milliliters, cups, and glasses.
How this calculation works
This calculator uses the widely cited guideline of about 33 ml of water per kilogram of body weight as a baseline daily fluid need for a sedentary adult in a temperate climate.
It then adds roughly 12 ml per minute of moderate physical activity to cover extra fluid lost through sweat, since exercise and heat both raise how much water your body needs.
The total in milliliters is converted to liters, standard 240 ml cups, and 250 ml glasses so you can track intake however is easiest for you.
Worked example
Why body weight drives the estimate
Larger bodies have more tissue, more blood volume, and a higher metabolic rate, all of which raise baseline fluid turnover. That is why hydration guidelines are usually expressed per kilogram of body weight (commonly 30–35 ml/kg) rather than as one fixed number for every adult.
This calculator uses 33 ml/kg as a practical midpoint, then layers on an activity allowance since sweat losses during exercise can easily exceed baseline needs on their own.
Typical daily fluid needs by activity level
| Activity level | Approx. daily activity | Extra fluid guidance |
|---|---|---|
| Sedentary | 0–15 min | Baseline weight-based amount only |
| Lightly active | 20–40 min | Add roughly 250–500 ml |
| Moderately active | 45–75 min | Add roughly 500–900 ml |
| Very active / hot climate | 90+ min or heat exposure | Add 1 L or more; monitor urine color |
Signs you need more (or less) water
- Dark yellow or amber urine usually signals it is time to drink more; pale straw-colored urine suggests adequate intake.
- Thirst, dry mouth, headache, and fatigue are early dehydration signs — don't wait until you feel very thirsty to drink.
- Frequent, clear urination and no thirst generally mean you are well hydrated or possibly overhydrated if extreme.
- Hot, humid weather, fever, vomiting, diarrhea, and high-altitude travel all raise fluid needs above the calculated baseline.
What this calculator does not account for
This tool gives a general population estimate, not personalized medical advice. It does not factor in pregnancy, breastfeeding, kidney or heart conditions, medications, or extreme environments, all of which can shift fluid needs significantly.
If you have a medical condition that affects fluid balance — such as kidney disease or heart failure — follow your doctor's specific fluid guidance instead of a general calculator.