Water Intake Calculator – How Much Water Should YOU Drink a Day?
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Calculate your daily water goal
Formula used: weight (kg) × 35 ml for adults (× 30 ml under 18), plus activity: sedentary 0 ml, light 350 ml, moderate 700 ml, active 1,050 ml, athlete 1,400 ml; plus climate: cool 0 ml, moderate 0 ml, hot 350 ml, very hot 700 ml; plus pregnancy 300 ml or breastfeeding 700 ml; minus 10% for age 56+. The result is rounded to the nearest 10 ml. This is a general estimate, not a medical prescription.
Recommended daily total fluids by group
These are the U.S. National Academies of Sciences, Engineering, and Medicine Adequate Intake values for total water from all drinks and food, not plain water alone. About 20% usually comes from food.
| Group | Total fluids per day |
|---|---|
| Adult men | 3.7 L (125 oz) |
| Adult women | 2.7 L (91 oz) |
| Pregnant women | 3.0 L (101 oz) |
| Breastfeeding women | 3.8 L (128 oz) |
Quick-reference daily water by weight
This table uses exactly the same formula as the calculator above, for an adult aged 18–55 in a moderate climate, with no pregnancy or breastfeeding adjustment. The Athlete / hot climate column adds athlete activity (1,400 ml) plus hot climate (350 ml) — not very hot climate (700 ml) — so a calculator result with very hot climate will be 350 ml higher than this column. That is why the calculator and the table now agree: for example, 70 kg with moderate activity is 3.15 L in both.
| Weight | Sedentary | Moderate activity | Athlete / hot climate |
|---|---|---|---|
| 50 kg / 110 lbs | 1.75 L (59 oz) | 2.45 L (83 oz) | 3.50 L (118 oz) |
| 60 kg / 132 lbs | 2.10 L (71 oz) | 2.80 L (95 oz) | 3.85 L (130 oz) |
| 70 kg / 154 lbs | 2.45 L (83 oz) | 3.15 L (107 oz) | 4.20 L (142 oz) |
| 80 kg / 176 lbs | 2.80 L (95 oz) | 3.50 L (118 oz) | 4.55 L (154 oz) |
| 90 kg / 198 lbs | 3.15 L (107 oz) | 3.85 L (130 oz) | 4.90 L (166 oz) |
| 100 kg / 220 lbs | 3.50 L (118 oz) | 4.20 L (142 oz) | 5.25 L (178 oz) |
Why the “8 glasses a day” rule is wrong for most people
Eight 8-ounce glasses is about 1.9 litres. It is a useful starting point, but it does not account for body size, exercise, heat, pregnancy or breastfeeding.
Signs you may not be drinking enough
- Dark yellow urine — aim for pale straw colour
- Afternoon fatigue and brain fog
- Frequent headaches, dry mouth, or muscle cramps
- Thirst mistaken for hunger
When you need more water than usual
- Exercise, especially in heat
- Hot weather, high altitude, or air travel
- Illness with fever, vomiting or diarrhoea
- Pregnancy and breastfeeding
- High-protein diets
Can you drink too much water?
Yes. Drinking more than about 1 litre per hour for several hours can dilute blood sodium and cause hyponatremia, which can be serious. Spread your intake across the day and do not gulp very large volumes at once.
Tips to reach your goal
- Drink a glass soon after waking
- Carry a 1-litre bottle and track refills
- Drink with meals and during exercise
- Eat water-rich foods such as cucumber, watermelon and soup
- Replace one sugary drink a day with water
Frequently asked questions
How much water should I drink a day?
Most adult men need about 3.7 L and women about 2.7 L of total fluids daily. Use the calculator for your personal number.
Is 8 glasses of water a day enough?
For a smaller, sedentary adult, yes. For larger adults, athletes, or hot climates, you will likely need more.
How is daily water intake calculated?
See the formula below the calculator. It starts with body weight and adds activity, climate, pregnancy or breastfeeding adjustments.
Do coffee, tea and juice count toward water intake?
Yes. Aim for at least 60% of daily fluid from plain water.
Can I drink too much water?
Yes. More than about 1 litre per hour for several hours can be harmful. Spread intake evenly through the day.
Sources and references
- U.S. National Academies of Sciences, Engineering, and Medicine — Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate (2004): Adequate Intake values quoted above.
- Mayo Clinic — “Water: How much should you drink every day?”: the same National Academies figures, with about 20% of fluid usually coming from food.
Last updated: 24 October 2026. All calculations run in your browser. No data is sent to a server and no account is required.