A practical starting point is about 33 milliliters of water for every kilogram you weigh, plus extra for exercise. A 70 kg (154 lb) adult who exercises one to three days a week needs about 70 × 0.033 = 2.31 liters, plus 0.35 liters for activity: 2.66 liters a day. That is roughly 11 cups, or a little over five 500 ml bottles.
Our free water intake calculator runs that estimate from your weight and activity level and shows the answer in liters, cups and bottles. This guide explains the formula, how it compares with official guidelines, and when you need more or less than the estimate.
How much water should you drink a day?
There is no single number that fits everyone. The US National Academies set an adequate daily intake of total water, from all drinks and food, of about 3.7 liters for men and 2.7 liters for women. Food usually supplies around a fifth of that, which leaves about 3.0 liters (13 cups) from drinks for men and 2.2 liters (9 cups) for women.
The familiar "8 × 8" rule, eight 8-ounce glasses, adds up to about 1.9 liters. It is easy to remember but has no scientific basis, and it ignores body size. A weight-based estimate scales with your body, which is why the calculator starts there.
How the calculator estimates your intake
Water per day (L) = Body weight (kg) × 0.033 + Activity allowance| Activity level | What it means | Added water |
|---|---|---|
| Low | Sedentary: little to no exercise | 0 L |
| Moderate | Light exercise, 1–3 days a week | 0.35 L |
| High | Moderate exercise, 3–5 days a week | 0.7 L |
| Extreme | Hard exercise, 6–7 days a week | 1.0 L |
Worked example: 70 kg with moderate activity
- Base amount: 70 × 0.033 = 2.31 liters.
- Add the Moderate allowance: 2.31 + 0.35 = 2.66 liters.
- In US cups of about 237 ml: 2.66 × 4.227 = 11.2 cups.
- In 500 ml bottles: 2.66 × 2 = 5.3 bottles.
In US units, 0.033 liters per kilogram works out to about half a fluid ounce per pound of body weight, which matches a rule of thumb many people already know.
Daily water by weight and activity
| Body weight | Low | Moderate | High | Extreme |
|---|---|---|---|---|
| 50 kg (110 lb) | 1.65 L | 2.00 L | 2.35 L | 2.65 L |
| 60 kg (132 lb) | 1.98 L | 2.33 L | 2.68 L | 2.98 L |
| 70 kg (154 lb) | 2.31 L | 2.66 L | 3.01 L | 3.31 L |
| 80 kg (176 lb) | 2.64 L | 2.99 L | 3.34 L | 3.64 L |
| 90 kg (198 lb) | 2.97 L | 3.32 L | 3.67 L | 3.97 L |
| 100 kg (220 lb) | 3.30 L | 3.65 L | 4.00 L | 4.30 L |
What counts toward your daily water
- All drinks. Water, milk, juice, tea and coffee all count. Caffeine has a mild diuretic effect, but moderate amounts of tea and coffee still add to your fluid intake overall.
- Food. Fruit, vegetables, soup and yogurt are mostly water. Cucumber, lettuce, watermelon and strawberries are over 90% water.
- What to limit. Sugary drinks add calories without extra benefit, and alcohol increases fluid loss.
When you need more, or less
The calculator gives a general estimate for healthy adults. Individual needs vary, and it does not account for:
- Heat and humidity. Hot weather and high altitude raise fluid losses through sweat and breathing.
- Illness. Fever, vomiting and diarrhea all increase how much you need to replace.
- Pregnancy and breastfeeding. The National Academies suggest about 3.0 liters of total water a day during pregnancy and 3.8 liters while breastfeeding.
- Long or intense exercise. Weigh yourself before and after a long session. Each kilogram lost is about a liter of sweat, and drinking around 1.5 liters for every kilogram lost helps you recover.
- Medical conditions. Some heart, kidney and liver conditions require limiting fluids. If you have one, follow your doctor's advice rather than any calculator.
Drinking far more than you need is also possible. Healthy kidneys can clear roughly a liter of water an hour, and drinking much faster than that over several hours can dilute the sodium in your blood, a condition called hyponatremia. It is rare, and most often seen in endurance events.
Signs to watch
Thirst and pale yellow urine usually mean you are drinking enough. Dark yellow urine, headache, tiredness and dizziness can be signs that you need more fluid.
How to use the water intake calculator
- Open the water intake calculator.
- Enter your Body weight in kilograms. If you know your weight in pounds, divide by 2.205 or use the weight converter: 154 lb is about 70 kg.
- Choose your Daily activity level: Low, Moderate, High or Extreme. A short description of the selected level appears under the buttons.
- Read Water per day in liters, with the same amount in US cups and 500 ml bottles. For fluid ounces or other units, enter the liters in the volume converter.
Tips for drinking enough
- Use a bottle you can count. If your target is 2.66 liters, a 1-liter bottle refilled two and a half times is easier to track than glasses.
- Tie drinking to routines. Have a glass with each meal and one when you wake up. If you work in focused blocks with a Pomodoro timer, refill your glass on every break.
- Front-load your day. Drink more in the morning and afternoon so you are not catching up late in the evening.
- Adjust for the day you are having. Recalculate with a higher activity level on training days or during a heat wave.
Frequently asked questions
How much water should I drink a day?
A common estimate is 33 ml per kilogram of body weight plus extra for exercise. A 70 kg adult with moderate activity needs about 2.66 liters, or 11 cups. Needs vary with climate, health and activity.
How much water should I drink based on my weight?
Multiply your weight in kilograms by 0.033 to get liters, then add an allowance for exercise. In US units that is about half a fluid ounce per pound, so a 160 lb person starts at around 80 ounces.
Do coffee and tea count toward water intake?
Yes. Moderate amounts of coffee and tea count toward your daily fluids despite their caffeine. Water from food, such as fruit, vegetables and soup, counts too.
How many cups is 2.5 liters of water?
About 10.6 US cups, since one liter is about 4.2 cups of 237 ml. It is also five 500 ml bottles.
Can you drink too much water?
Yes, though it is rare. Drinking much more than your kidneys can clear, roughly a liter an hour, for several hours can cause hyponatremia, a dangerous drop in blood sodium. Spread your intake across the day.
Can I enter my weight in pounds?
No, the calculator takes kilograms only. Divide your weight in pounds by 2.205 first: 154 lb is about 70 kg.