Water Intake Calculator
Estimate how much water to drink daily based on body weight and activity.
Inputs
Allowed range: 10 to 600
Allowed range: 0 to 600
Results
How it works
Baseline ≈ 35 ml per kg of body weight, plus ~500 ml for every 30 minutes of exercise.
Complete guide
Hydration needs vary with body size, activity, climate, and diet. The popular '8 glasses a day' rule is a rough average — a 50 kg sedentary office worker and a 100 kg construction worker in summer have very different needs.
A common evidence-based estimate is 30–40 ml of total water per kilogram of body weight per day, plus about 500 ml extra for every 30 minutes of moderate exercise. Roughly 20% of that comes from food (especially fruits, vegetables, and soup), so the rest needs to come from drinks.
Reliable signs you're well hydrated: pale-yellow urine, no constant thirst, normal energy. Dark urine, headache, or fatigue often signal mild dehydration.
Frequently asked questions
- Does coffee or tea count?
- Yes. Despite the old myth, the mild diuretic effect of caffeine doesn't outweigh the water in the cup. Water, milk, juice, soup, and watery foods all contribute.
- Can I drink too much water?
- Rarely, but yes. Drinking several liters in a short time can dilute blood sodium dangerously (hyponatremia), especially in endurance athletes. Spread intake across the day.
- Should I drink more in hot weather?
- Yes — sweating loses fluid and electrolytes. Add 500–1,000 ml on hot days and consider an electrolyte drink for heavy sweating over an hour.
- Is this the same for kids and pregnant women?
- No. Children need less in absolute terms but more per kg of body weight. Pregnancy and breastfeeding increase needs by roughly 300–700 ml/day. Ask a clinician for a personalized number.