Articles · Health & Science
Daily Water Intake by Body Weight: How Much Per kg?
If you have ever searched how much water should I drink per kg of body weight, you are not alone. Generic "eight glasses a day" advice ignores that a 55 kg desk worker and a 90 kg athlete do not share the same fluid needs. A practical starting point used by many coaches and apps—including our hydration calculator—is roughly 30–35 ml per kg of body weight per day from beverages, before adjusting for climate, activity, and diet.
The weight-based formula in plain English
Multiply your weight in kilograms by 0.03 to get a baseline in liters (about 30 ml/kg). Someone at 70 kg lands near 2.1 liters of fluids; at 85 kg, closer to 2.5 liters. That is a starting estimate, not a ceiling. Hot weather, pregnancy, illness, and long workouts push needs higher. People who eat lots of soup, fruit, and vegetables may need slightly less from the tap because food contributes to total water intake—see our broader guide on how much water per day for context.
When to adjust up or down
Increase intake when you sweat heavily, live at altitude, or feel early dehydration signs. Decrease only with clinician guidance—kidney or heart conditions sometimes require fluid limits. Avoid chasing extreme gallon challenges; read about overhydration and water intoxication if you are pushing far beyond thirst.
Make the number stick with habits
Knowing your kg-based target is step one; spreading sips across the day is step two. TakeSip on macOS turns your personalized goal into gentle reminders so you are not chugging a liter at bedtime. Recalculate after major weight changes or when your training load shifts.
Pounds vs kilograms
If you think in pounds, divide your weight by 2.2 to convert to kg first, or use roughly half an ounce per pound as a rough U.S. shorthand—about 75 oz for a 150 lb person. The exact number matters less than checking whether you feel better at your calculated baseline versus your old habit. Log a week at the new target, note energy and urine color, then tweak. Athletes in heavy training often add 500 ml–1 L on top of body-weight math without guilt.
Who should not use weight formulas alone
Heart failure, kidney disease, and certain medications require clinician-set fluid limits—weight math is a starting point for healthy adults, not a prescription for everyone. Pregnancy and breastfeeding increase needs beyond kg formulas; follow OB guidance. When in doubt, ask a professional rather than scaling linearly forever.