Water Intake Calculator

The commonly cited "8 glasses a day" guideline is a rough approximation. A more accurate method is to base your intake on body weight: roughly 33ml per kilogram of body weight. For a 70kg adult that is about 2.3 liters, but activity level and climate can push that figure significantly higher. This calculator applies those adjustments automatically.

Yes, significantly. During exercise you lose water through sweat and respiration. A moderate workout can add 500ml or more to your needs, while an intense session or endurance sport can require 1–2 extra liters. Always drink before you feel thirsty — thirst is a late signal of dehydration. This calculator boosts your target by 20–60% depending on your chosen activity level.

Partially. Coffee and tea do contribute to overall fluid intake, but caffeine has a mild diuretic effect that offsets some of the benefit. A good rule of thumb is to count caffeinated drinks at about 50–75% of their volume toward your daily target, and for every cup of coffee drink an extra half cup of plain water to compensate.

Hot or humid weather increases sweat rate even at rest, raising your baseline requirement by 500–1000ml per day. High altitude also increases fluid loss through faster breathing. Selecting "Hot / Humid" in the calculator adds 500ml to your daily total to reflect this. On particularly hot days or after outdoor activity in the heat, consider drinking even more.