Daily Water Intake Calculator
Even mild dehydration — just 1–2 % of your body weight — slows your metabolism, reduces fat oxidation, and mimics hunger. This calculator combines the weight-based formula (30–35 ml per kg) with the Institute of Medicine reference values to give you a personalised daily hydration target.
Adjust for your activity level and hot weather to get an accurate estimate. Results include a glass count, a breakdown of each factor, and a suggested hourly distribution across your waking day.
Water Intake Calculator
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ml / day
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glasses of 250 ml
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Base (weight)
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Activity
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💧 IoM reference (total fluid incl. food):
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Suggested daily schedule
The Science Behind the Calculator
Weight-based formula: Research supports a daily fluid intake of 30–35 ml per kg of body weight. Men have a slightly higher lean mass and sweat rate — this calculator uses 35 ml/kg for men and 31 ml/kg for women as the baseline.
Institute of Medicine (IoM) targets: The IoM recommends 3,700 ml/day for men and 2,700 ml/day for women as total fluid intake (drinks and food). About 20% of daily fluid comes from food, so the pure drink target is ~3,000 ml for men and ~2,200 ml for women.
Activity adjustment: You lose 350–700 ml per hour of exercise through sweat. The calculator adds 175 ml for each activity increment from light (0.5 h) to very active (2 h/day).
Connection to weight management: Water is required for lipolysis (fat breakdown). Dehydration of just 1% reduces metabolic rate. Drinking 500 ml before meals has been shown to reduce calorie intake and support weight loss.
Water Intake — Frequently Asked Questions
How much water should I drink per day?
The general guideline is 30–35 ml per kg of body weight per day. A 70 kg person needs about 2,300 ml (roughly 9 glasses). The Institute of Medicine recommends 3,700 ml total for men and 2,700 ml for women (including water from food).
Does physical activity affect water intake?
Yes. You lose 350–700 ml of fluid per hour of exercise through sweat. Add that amount on top of your daily baseline. Active athletes training twice a day may need 5,000 ml or more.
Does hot weather increase water needs?
Yes. In temperatures above 30°C your body sweats more to cool down. Add at least 500 ml on hot days, and more if you are outdoors or exercising in the heat.
Can dehydration affect weight loss?
Yes. Even mild dehydration (1–2% of body weight) slows metabolism, reduces fat oxidation, and is often confused with hunger. Drinking enough water supports satiety and metabolic function.
Does coffee or tea count toward daily water intake?
Moderate coffee and tea consumption does contribute to hydration. The diuretic effect of caffeine is mild and does not cancel out the fluid consumed. However, plain water remains the best source of hydration.
