Water Intake Calculator
Find how much water to drink each day based on your body weight and activity level.
How to Use the Water Intake Calculator
Staying properly hydrated supports energy, focus, digestion, and temperature regulation. This tool estimates a sensible daily drinking-water target for you:
- Enter your body weight in kilograms.
- Select your activity level — more exercise means more fluid lost through sweat.
- Read your goal in litres, millilitres, and 250 ml glasses.
How the Estimate Works
A widely used guideline is roughly 35 ml of water per kilogram of body weight, with extra added for exercise. This calculator uses:
Daily Water (ml) = Weight (kg) × 35 + Activity Adjustment
Activity adjustment: Sedentary +0 · Light +350 ml · Moderate +700 ml · Very Active +1050 ml
Worked Example
Example: 70 kg Adult, Moderately Active
Step 1 — Base: 70 × 35 = 2,450 ml
Step 2 — Add activity: Moderate = +700 ml → 2,450 + 700 = 3,150 ml
Result: about 3.15 litres a day, or roughly 13 glasses of 250 ml each.
Recommended Water by Body Weight
Here is the estimated daily water goal at a moderate activity level for a range of body weights:
| Body weight | Daily water (moderate activity) | Glasses (250 ml) |
|---|---|---|
| 50 kg | 2.45 litres | ~10 |
| 60 kg | 2.8 litres | ~11 |
| 70 kg | 3.15 litres | ~13 |
| 80 kg | 3.5 litres | ~14 |
| 90 kg | 3.85 litres | ~15 |
Tips to Stay Hydrated
- Start early: Drink a glass of water when you wake up to rehydrate after sleep.
- Keep a bottle visible: A reusable bottle on your desk is a simple, effective reminder.
- Drink more when it's hot or you exercise: Replace fluids lost through sweat.
- Watch your urine colour: Pale, straw-coloured urine usually means you are well hydrated.
- Don't rely on thirst alone: By the time you feel thirsty, you may already be mildly dehydrated.
Frequently Asked Questions
A common guideline is about 30–35 ml of water per kilogram of body weight, plus extra for exercise. For a 70 kg adult that is roughly 2.5–3 litres a day. Needs rise in hot weather, during illness, and with physical activity.
Yes. Around 20% of your total fluid typically comes from food — fruits, vegetables, soups, and other moisture-rich foods. This calculator estimates your drinking-water target; total fluid needs are slightly higher and partly met by food.
Rarely, but yes. Drinking very large amounts in a short time can dilute blood sodium (hyponatraemia), which is dangerous. Spread your intake through the day rather than consuming it all at once.
They contribute to hydration despite a mild diuretic effect. Water, however, is the best choice because it has no sugar, calories, or caffeine. Sugary drinks should not be your main hydration source.
Pale, straw-coloured urine and infrequent thirst are good signs. Dark urine, dry mouth, headache, or fatigue can indicate you need more fluids.
Sources & References:
- World Health Organization (WHO) - Global health metrics and standards.
- Centers for Disease Control and Prevention (CDC) - Anthropometric reference data and healthy weight guidelines.
- National Institutes of Health (NIH) - Clinical guidelines for the identification, evaluation, and treatment of overweight and obesity.
- Mifflin-St Jeor, Boer, and US Navy established mathematical models for body composition and metabolic rate estimation.
Sources & References
- U.S. National Academies of Sciences, Engineering, and Medicine: Dietary Reference Intakes for water (about 3.7 L/day total for men, 2.7 L/day for women, including water from food).
- Harvard T.H. Chan School of Public Health: The Nutrition Source — Water
Health Disclaimer: This water intake calculator provides a general estimate for healthy adults and is for educational purposes only. Individual needs vary with climate, health conditions, pregnancy, medications, and kidney or heart conditions. It is not medical advice. Consult a qualified healthcare professional for personalised guidance.