Water Intake Calculator

A widely used formula is 0.033L per kg of body weight. A 70 kg person needs about 2.3L (roughly 9-10 cups) at rest. The National Academies of Sciences recommend about 3.7L total water for men and 2.7L for women including water from food (which accounts for ~20%). Individual needs vary significantly with activity, heat, and health.

The "8×8" rule (eight 8-oz glasses = about 2L) is a rough guideline with no strong scientific basis — it ignores your weight, activity level, and climate. Use this calculator for a personalised estimate instead. A lighter, sedentary person in a cool climate may need less; a large, active person in hot weather needs considerably more.

Yes — caffeinated beverages still contribute to your fluid intake despite caffeine's mild diuretic effect. Studies show the net hydration effect of coffee and tea is positive, not negative. However, water, herbal teas, and diluted juice are the most efficient sources. Alcohol is dehydrating and should not be counted.

The simplest indicator is urine colour: pale yellow (like lemonade) means well-hydrated; dark yellow or amber means drink more water. Clear urine can indicate over-hydration. Other signs of dehydration include headache, fatigue, dry mouth, and reduced urine frequency (fewer than 4–5 times per day).

Yes. Pregnant women are typically advised to drink an additional 0.3L (1.5 cups) per day. Breastfeeding women need an extra 0.7–1L per day since breast milk is about 87% water. The calculator includes these adjustments automatically when you select the relevant option.