Eight glasses a day?
That rule ignores body size. Weight-based estimates are more personalized.
Water Intake Calculator
Estimate how much water to drink daily based on body weight and how active you are.
Daily water needs
Enter body weight and pick an activity level for a practical hydration target.
About this calculator
How to use Water Intake Calculator, plus the formulas and logic behind the results.
Tool description
Hydration needs vary with size, climate, and sweat loss. This uses a simple weight-based baseline plus an activity bump—not a medical prescription.
How to use
- Enter weight in kg or lb.
- Choose how sweaty or active your typical day is.
- Review ml, liters, and cup estimates.
- Drink steadily through the day; thirst and urine color are useful checks.
Formulas & reference
Base ≈ 35 ml × body weight (kg)Activity bonus: 0–1000 ml depending on level
Hydration tips
- Pale yellow urine often indicates adequate hydration
- Spread intake across the day
- Extra fluid around workouts and in heat
- Food also contributes to total water intake
Calculation logic
Weight converts to kg. Base intake scales at 35 ml/kg, then a fixed bonus is added for activity level.
Pregnancy, breastfeeding, fever, and hot climates may need more fluid than this estimate.
Water Intake Calculator FAQ
Common questions about this calculator and how to use the results.
Count coffee and tea?
Mild diuretic effect exists, but caffeinated drinks still contribute to fluid intake for most people.
Exercise?
Pick a higher activity level or add 500 ml+ around long or sweaty sessions.
Liters vs cups?
Results show ml, liters, and US cups for convenience.
Too much water?
Rare in healthy adults, but medical conditions can require fluid limits—ask your doctor.
Electrolytes?
Long endurance sessions in heat may need sodium, not just plain water.