How much water should I drink per day?

Daily water intake varies depending on body weight, activity level, and climate. Many health experts recommend around 30–40 ml of water per kilogram of body weight per day.

How does a water intake calculator work?

A water intake calculator estimates hydration needs based on body weight and activity level. It multiplies weight by an average hydration factor to estimate daily fluid intake.

What is the formula for daily water intake?

A common hydration formula is: Daily Water Intake = Body Weight (kg) × 30–40 ml.

Why is drinking enough water important?

Adequate hydration supports digestion, circulation, body temperature regulation, brain function, and physical performance.

Does body weight affect water intake?

Yes. Larger body mass generally requires more water because metabolic processes and fluid distribution increase.

Does exercise increase water needs?

Yes. Exercise causes fluid loss through sweat, so additional water is needed to maintain hydration.

Does hot weather affect hydration requirements?

Yes. Hot and humid climates increase sweat loss, which raises daily water intake needs.

Water Intake Calculator — How Much Water Should You Drink Per Day?Daily Water Intake · ml & Litres · Body Weight · Activity Level · Climate

Use this free Water Intake Calculator to instantly estimate your recommended daily water intake in ml, litres, and glasses per day — personalized to your body weight, physical activity level, and climate conditions. Based on the widely referenced hydration formula of 35ml per kg of body weight and WHO and NHS daily water intake guidelines, this daily water calculator computes your baseline hydration needs then adjusts for: sedentary, lightly active, moderately active & highly active lifestyles · hot & humid vs cool climate water loss adjustment · exercise & workout additional hydration requirements — giving you a precise daily water intake target in litres, ml, and number of 250ml glasses.

Proper daily hydration is one of the most impactful factors in overall health and wellbeing, directly supporting digestive function and nutrient absorption, cardiovascular circulation and blood pressure regulation, kidney function and toxin elimination, body temperature regulation and thermoregulation, cognitive performance, concentration and mental clarity, joint lubrication and physical performance, and skin health and cellular hydration. Signs of dehydration include dark urine, fatigue, headaches, dry mouth, and reduced concentration — while overhydration (hyponatremia) is a risk for endurance athletes consuming excessive water without electrolyte replacement. This water intake calculator is trusted by fitness enthusiasts, athletes, dietitians, healthcare professionals, and anyone tracking their daily water consumption for better health, weight loss, sports performance, and skin care goals.

⚠ Health Disclaimer: This water intake calculator provides general hydration guidelines for informational and wellness purposes only. Individual daily water requirements vary based on age, body composition, pregnancy or breastfeeding status, underlying medical conditions (kidney disease, heart failure, diabetes), medications affecting fluid retention, dietary water content from food, and caffeine and alcohol consumption. People with chronic health conditions should consult a doctor, registered dietitian (RD), or nephrologist for personalized hydration and fluid intake recommendations.

Weight (kg)

Activity Level

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Water Intake Calculator — How Much You Actually Need Based on Weight and Activity

The "8 glasses of water per day" rule has no scientific basis — it was derived from a 1945 recommendation that was misread to exclude the water in food, which provides 20-30% of daily hydration. Evidence-based hydration needs scale with body weight and activity. A general baseline for sedentary adults is 30-35 mL/kg/day: a 70 kg person needs approximately 2.1-2.45 liters. Exercise adds roughly 500-750 mL per hour of moderate activity; hot weather adds 250-500 mL/day; altitude adds another 500-750 mL/day as respiratory losses increase.

Urine color is the most practical hydration feedback for daily life — pale yellow indicates adequate hydration; dark yellow or amber indicates dehydration; colorless indicates excess hydration. Electrolyte depletion from excess water intake (hyponatremia) is a real clinical concern for endurance athletes who drink large volumes without replacing sodium. The calculator provides total fluid targets and notes that coffee, tea, and food moisture all count toward daily fluid intake — the "coffee dehydrates you" claim is largely a myth at moderate intake.

Pregnancy and breastfeeding substantially increase water needs. Pregnant women should increase intake by approximately 300-500 mL/day; breastfeeding women need 700-1000 mL/day extra because breast milk is 88% water. Hot climate work increases needs to 1 liter/hour or more during strenuous activity. The calculator adjusts baseline recommendations for these special circumstances and provides the hourly intake rate needed to meet daily targets for athletes planning competition hydration strategies.