Water Intake Calculator
Estimate your daily water needs from body weight, exercise, and climate.
How We Calculate This
The baseline figure here uses 30–35 mL of water per kg of body weight per day, a common clinical rule of thumb (we use the 33 mL/kg midpoint) rather than a figure drawn directly from a single authoritative study. It's a practical starting point, not a precise requirement — actual needs vary by person, diet, and activity.
For a more authoritative benchmark, the U.S. National Academies of Medicine (formerly the Institute of Medicine) set Adequate Intake levels for total water — from all beverages and food combined — at about 3.7 L/day for men and 2.7 L/day for women. EFSA, the European Food Safety Authority, set its own Adequate Intakes at about 2.5 L/day for men and 2.0 L/day for women under moderate temperature and activity conditions. Both bodies agree that people who exercise heavily or live in hot climates need more than these baseline figures.
Exercise adjustment: we add fluid using the American College of Sports Medicine's position stand on exercise and fluid replacement, which recommends replacing losses at a rate of roughly 600–1200 mL per hour of exercise; we use a conservative 700 mL/hour estimate. Sweat rates vary a great deal between individuals and conditions, so treat this as a reasonable estimate rather than an exact figure — heavy or salty sweaters may need more, and pairing this with electrolytes matters for exercise over about an hour. Read more on that in our electrolytes page.
Climate adjustment: selecting "Hot / Humid" adds a flat 500 mL/day, a practical estimate reflecting the higher sweat losses of hot conditions — the National Academies' own guidance explicitly notes that people in hot climates may need more than the baseline Adequate Intake, though it does not specify an exact additional figure.
Read EFSA's Scientific Opinion on Dietary Reference Values for water →
Source: Sawka MN, et al. "American College of Sports Medicine Position Stand: Exercise and Fluid Replacement," Medicine & Science in Sports & Exercise.
Read the ACSM position stand →
Exercising for more than an hour, especially in the heat? Sodium and other electrolytes matter alongside plain water — see our Electrolytes guide for who actually needs them.