How this estimate works
The baseline uses 35 ml of total water per kilogram of body weight — a figure from the U.S. National Academies' reference intakes (3.7 L/day for men, 2.7 L/day for women, from all sources). On top of the baseline, each 30 minutes of exercise adds roughly 350–400 ml to replace sweat losses, and hot or humid climates add about 500 ml.
Food counts too: roughly 20% of most people's water intake comes from food, and other beverages contribute as well. The number below is total water for the day — drink it as plain water, or split it however you prefer.
Signs you are drinking enough
- Pale straw-colored urine, and urinating every 2–4 hours
- No persistent thirst, headache or afternoon fatigue
Drinking far beyond thirst during endurance events can be dangerous (hyponatremia). People with kidney or heart conditions should follow their clinician's fluid limits instead of general formulas.