A general estimate (about 33 ml per kg of body weight plus exercise and climate). Needs vary with health, pregnancy and medication. Ask your doctor if you have a medical condition.
How Much Water Should You Drink Every Day?
Water makes up around 50 to 60 percent of an adult body. It carries nutrients, cushions joints, helps regulate temperature, supports digestion and keeps your brain sharp. You lose water all day through breathing, sweat and urine, so you need to replace it. The right amount is different for everyone, which is why a single rule such as eight glasses a day only goes so far. Our Daily Fluid Intake Calculator gives you a personal estimate based on your weight, exercise and climate.
How the Calculator Estimates Your Needs
The tool starts with a widely used baseline of about 33 millilitres of fluid per kilogram of body weight. It then adds about 12 millilitres for each minute of exercise, which is roughly 350 ml for 30 minutes of activity, and 500 ml extra if you live or work in a hot or humid place. The answer is shown in litres, fluid ounces and cups so you can pick whichever is easiest to follow.
For example, a person who weighs 70 kg and exercises for 30 minutes in a mild climate needs about 2.3 litres plus 0.36 litres, or roughly 2.7 litres a day. That total includes water from all drinks and from food.
Does All of It Need to Come From Plain Water?
No. About 20 percent of daily fluid comes from food. Fruit and vegetables such as watermelon, cucumber, oranges, lettuce and tomatoes are more than 85 percent water. Soup, milk, yogurt, tea and coffee also count. Plain water is still the best choice because it has no calories or sugar. If you find water boring, add lemon, mint, cucumber or a few berries. Be careful with sweetened drinks: use the Daily Sugar Intake Calculator to see how quickly a soft drink or energy drink uses up your limit.
Signs You May Not Be Drinking Enough
- Dark yellow or strong-smelling urine
- Thirst, dry mouth or cracked lips
- Headache or trouble concentrating
- Tiredness and dizziness, especially when standing up
- Constipation
- Muscle cramps during exercise
Pale yellow urine is a simple, reliable sign that you are well hydrated.
Can You Drink Too Much?
Yes, though it is rare. Drinking a very large amount in a short time can dilute sodium in the blood, a condition called hyponatremia. It mostly affects endurance athletes and people with certain kidney, heart or hormone conditions. Sip steadily through the day instead of forcing large volumes, and stop if you feel sick or bloated.
When You Need More Fluid
- Hot weather, humidity or high altitude
- Hard or long exercise, especially over an hour
- Fever, vomiting or diarrhea
- Pregnancy and breastfeeding, when needs rise by roughly 300 to 700 ml per day
- A high-protein diet, which asks the kidneys to work harder (see our Protein Requirements Calculator)
- High-fiber diets, which need extra water to work well
Easy Ways to Build a Hydration Habit
- Start the day with a glass of water before coffee
- Keep a refillable bottle on your desk or in your bag
- Drink a glass with every meal and snack
- Set reminders on your phone for the afternoon, when intake often drops
- Eat water-rich foods such as soups, fruit and salads
- Drink a little extra before, during and after exercise
Hydration, Weight and Energy
Thirst is sometimes mistaken for hunger, and a glass of water before a meal can help some people eat a little less. Water does not burn fat on its own, but replacing sugary drinks with water can cut hundreds of calories a day. Check your total needs with the Daily Caloric Needs Calculator and see where you stand with the BMI Calculator.
Hydration for Older Adults and Children
The sense of thirst weakens with age, so older adults can become dehydrated without feeling thirsty. They should drink regularly through the day. Children lose water quickly when they play and have a smaller reserve, so offer water often, especially in warm weather and during sports. The estimate on this page is intended for adults.
Frequently Asked Questions
Do coffee and tea count toward my fluid goal?
Yes. Moderate amounts of caffeine have only a mild diuretic effect, and the water in the drink more than makes up for it.
Is eight glasses a day correct?
It is a handy rule of thumb, roughly 1.9 litres, but your own number may be higher or lower depending on size, activity and climate.
Should I drink sports drinks?
For most workouts under an hour, water is enough. Sports drinks help during long or very intense exercise when you lose a lot of salt.
This tool provides a general estimate for healthy adults and is not medical advice. If you have kidney, heart or liver disease, take diuretics or have been told to limit fluids, follow your doctor’s guidance.
Key Takeaways About Hydration
- A good starting point is about 33 ml of fluid per kg of body weight, plus extra for exercise and heat.
- Around 20 percent of your fluid comes from food, and tea, coffee and milk count too.
- Pale yellow urine is a simple sign that you are well hydrated.
- Drink more in hot weather, during illness and when you exercise for long periods.
- Sip steadily through the day rather than drinking a huge amount at once.
If you are new to drinking more water, build up slowly. Add one extra glass a day for a week, then another, until you reach your goal. Many people find it easiest to link water with habits they already have, such as brushing teeth, starting the computer or finishing a meal. Carry a bottle you like, and refill it at set times so you always know how much you have had.