Water Intake Calculator

A water intake calculator estimates how much water you should drink per day based on your individual characteristics. The most widely used baseline in sports medicine is 35 ml per kilogram of body weight per day for a sedentary adult in a temperate climate. This baseline is then adjusted upward for physical activity (which causes sweat loss) and hot or humid climates (which increase fluid needs through perspiration). Our water intake calculator applies these adjustments to give you a personalized daily hydration goal in litres, millilitres, fluid ounces, and glass counts — all running instantly in your browser with no signup required.

1. Enter Your Weight and Select Units: Enter your body weight in kilograms (metric) or pounds (imperial). The water intake calculator converts pounds to kilograms internally for the calculation. Switch between unit systems using the toggle at the top.
2. Choose Activity Level and Climate: Select your typical activity level (sedentary to very intense) and your current climate (cold to very hot). The water intake calculator adds extra fluid for exercise and heat exposure on top of the baseline. All calculations happen locally in your browser — no data is sent to any server.
3. Read Your Personalized Results: The water intake calculator shows your total daily intake in litres, fluid ounces, and glass counts. The breakdown shows exactly how much each factor contributes. The hourly schedule shows how to spread your intake across 16 waking hours.

• Baseline (35 ml/kg): The foundation of the calculation. A 70 kg adult needs 70 × 35 = 2,450 ml (2.45 L) per day at rest in a temperate climate.
• Activity Adjustment: Light activity adds 350 ml, moderate adds 700 ml, intense adds 1,050 ml, and very intense adds 1,400 ml to account for sweat loss during exercise.
• Climate Adjustment: Cold climates subtract 250 ml (reduced sweat). Warm adds 250 ml, hot adds 500 ml, and very hot/tropical adds 750 ml to compensate for increased perspiration.
• Minimum Floor: The water intake calculator enforces a minimum of 1,500 ml (1.5 L) per day regardless of inputs, as this is the minimum required for basic kidney function.

The water intake calculator provides a general guideline based on widely accepted formulas. Individual needs vary based on health conditions, medications, diet (fruits and vegetables contain significant water), and other factors. Thirst is a reliable indicator of hydration needs for most healthy adults — drink when you feel thirsty and aim to keep urine pale yellow. People with kidney disease, heart failure, or other conditions affecting fluid balance should consult a healthcare professional for personalized hydration advice. The calculator does not account for water from food, which typically contributes 20–30% of total daily fluid intake.