Daily Water Intake Calculator
Find out exactly how many liters of water you should drink each day based on your body weight and how active you are. Use it when setting hydration goals or adjusting intake during exercise.
About this calculator
The calculator uses a widely cited guideline of 35 mL of water per kilogram of body weight per day as a baseline, then scales that figure by an activity multiplier to account for fluid lost through sweat and exertion. The formula is: daily intake (L) = (weight × 35 × activity) / 1000. A sedentary person typically uses an activity factor near 1.0, while someone doing intense daily exercise may use 1.4 or higher. Dividing by 1000 converts the result from milliliters to liters. This is a general guideline; individual needs vary with climate, health status, and diet. The 35 mL/kg rule aligns with recommendations from several European and international health bodies.
How to use
Suppose you weigh 70 kg and have a moderately active lifestyle (activity factor = 1.2). Plug into the formula: (70 × 35 × 1.2) / 1000 = 2,940 / 1000 = 2.94 liters per day. That means you should aim to drink roughly 3 liters of water daily. On days you exercise more intensely, raise the activity factor to 1.4: (70 × 35 × 1.4) / 1000 = 3.43 liters. Start with your resting weight and adjust the activity slider to match your typical day.
Frequently asked questions
How much water should I drink per day based on my body weight?
A commonly used rule is 35 mL of water per kilogram of body weight for a sedentary adult. For a 70 kg person that works out to about 2.45 liters at rest. Activity, heat, and individual health factors can push that number significantly higher. This calculator applies an activity multiplier so the result reflects your actual daily energy expenditure rather than a one-size-fits-all figure.
What activity level multiplier should I use for the water intake calculator?
A multiplier of 1.0 suits a largely sedentary lifestyle — desk work with little exercise. Light activity such as walking 30 minutes a day warrants around 1.2. Moderate gym sessions three to five times a week correspond to roughly 1.3–1.4. Endurance athletes or people working physically demanding jobs outdoors in heat may need 1.5 or above to compensate for sweat losses.
Why is drinking enough water important for overall health?
Water is involved in virtually every metabolic process: it regulates body temperature, transports nutrients, cushions joints, and supports kidney function. Even mild dehydration of 1–2% of body weight can impair concentration and physical performance. Chronic under-hydration is linked to kidney stones, urinary tract infections, and constipation. Tracking your daily target with a calculator helps turn an abstract recommendation into a concrete, achievable goal.