Your Exact Daily Water Need
Calculate in 10 seconds. Personalized for your weight, activity, and climate. Science-backed. Free, no signup required.
Quick answer
Most healthy adults need 30-40 ml of water per kilogram of body weight per day — about 2.0 L for a 60 kg person and 2.8 L for an 80 kg person. Add ~500 ml for each hour of exercise, ~500 ml for hot or humid weather, and more during pregnancy or breastfeeding. Use the calculator below for your exact number.
💧 Quick Hydration Check
Get your estimated daily water need in 10 seconds.
Estimate only. Consult a doctor for chronic conditions (CKD, heart failure, etc.).
How we calculate your number
Vari’s calculator uses the same formula trusted by the EFSA (European Food Safety Authority) and the U.S. Institute of Medicine for healthy adults:
+ activity_modifier (0 to 1000 ml based on activity level)
+ climate_modifier (0 to 600 ml based on temperature)
Activity modifier: sedentary desk job adds 0 ml; light exercise 250 ml; moderate (3-5 workouts/week) 500 ml; active (daily workouts) 750 ml; very active (athletes, 2x daily) 1000 ml.
Climate modifier: under 15°C adds 0 ml; 15-25°C adds 0 ml; 25-32°C adds 300 ml; 32°C+ adds 600 ml. Humidity above 70% effectively bumps you to the next tier.
What counts as water? Plain water, tea, coffee (up to 4 cups/day), milk, juice, and high-water foods (cucumber, watermelon, soup). The 8-glasses rule is folklore — your actual need depends on body size and lifestyle.
Frequently asked questions
How accurate is this hydration calculator?
The formula (35 ml per kg body weight + activity + climate modifiers) matches the EFSA European Food Safety Authority and U.S. Institute of Medicine baseline recommendations for healthy adults. It's an estimate — your exact need can vary based on diet, sleep, caffeine, and individual metabolism. For chronic conditions (CKD, heart failure), consult your doctor.
Why does Vari's calculator differ from the 8-glasses rule?
The '8 glasses a day' rule has no scientific basis — it's a 1945 footnote that became folklore. Your actual need scales with body weight, activity, and climate. A 55 kg office worker in a temperate climate needs about 1.9 L, while an 85 kg runner in hot weather needs closer to 3.7 L. A fixed number can't reflect that range.
Does coffee count toward my daily water intake?
Yes. Moderate caffeine intake (up to ~400 mg/day, roughly 3-4 cups of coffee) is net-hydrating — the water content outweighs the mild diuretic effect. Vari counts coffee, tea, and other drinks with the correct hydration factor automatically.
Should I drink more water when pregnant or breastfeeding?
Yes. Pregnancy adds about 300 ml per day and breastfeeding adds 500-700 ml per day, depending on how much milk you produce. The Vari app has specific pregnancy and breastfeeding health profiles that handle this automatically.
What if I have kidney disease?
CKD patients often have FLUID RESTRICTIONS, not the general guidance this calculator gives. Do not use a generic hydration calculator for CKD — follow your nephrologist's specific fluid limit. The Vari app has a CKD-aware profile that respects fluid restrictions.
Is the result the same as what I'll get in the Vari app?
The baseline daily total matches. The app adds: (1) an intelligent schedule that spreads your intake across the day, (2) real-time weather-based adjustments, (3) Apple Health integration that fine-tunes for sleep and workouts, and (4) reminders that actually fire when you need them.