Daily water intake recommendations are typically 30-45 mL per kg of body weight, adjusted for activity level. The calculator returns the figure in litres and as a count of standard 250 mL glasses. Aim for the higher end on hot days or after intense exercise.
What is Water Intake?
The '8 glasses a day' rule is folklore, not science. Actual hydration needs vary by body size, activity level, climate, diet, and overall health. A 50 kg sedentary person and a 90 kg athlete have very different requirements.
Most adults need 30-35 mL/kg of body weight on a typical day. That is 2.1-2.5 L for a 70 kg person. Active people, those in hot climates, and those eating very salty diets need more — up to 45 mL/kg. Pregnant or breastfeeding women have additional needs.
About 20% of fluid intake comes from food (especially fruits, vegetables, soups). The calculator gives total fluid intake — you do not need to drink all of it as plain water. Tea, coffee (yes, even with caffeine), milk, and juices all count toward the total.
Water intake formula
- Weight
- Body weight—in kilograms
- Activity factor
- Lifestyle multiplier—30/35/45 mL per kg based on activity
How to use this calculator
Two inputs: weight and activity level. Result is a daily target.
Enter your weight
Use kg. Body water needs scale with size — not just lifestyle.
Pick activity level
Sedentary = office job + no exercise. Moderate = ~30 min daily exercise. High = 1+ hour intense or hot-climate work.
Read the target
Total daily fluid intake in litres and glasses. Includes water from food and other beverages.
When the calculator is useful
Setting a water intake habit
Knowing the target makes it easier to commit. Buy a 1-litre bottle and aim for 2-3 refills.
Hot Indian summers
Northern India routinely hits 45°C in May-June. Add 500-1000 mL extra during peak heat.
Endurance training
Marathon training adds hundreds of extra mL per training session. Replace fluids and electrolytes.
Travel and altitude
Air travel and high altitude both increase fluid loss. Increase intake by ~500 mL on flying days.
Common mistakes to avoid
Counting only plain water
Tea, coffee, milk, soup, watermelon, cucumber — all contribute. The calculator's number is total fluid, not 'glasses of water'.
Ignoring kidney or heart conditions
Some medical conditions require fluid restriction. Always follow your doctor's advice over a generic calculator if you are managing a medical condition.
Glossary
- Hydration
- The state of having sufficient fluid in your body. Affects energy, focus, kidney function, and skin.
- Hyponatraemia
- Dangerously low blood sodium, caused by drinking large volumes of plain water without replacing salts.
- Electrolytes
- Sodium, potassium, magnesium, calcium — minerals lost in sweat and replaced via food or sports drinks.