General guideline (~33ml per kg body weight, plus extra for exercise). Needs vary with climate, health and diet — consult a doctor for personalized advice.
What is a water intake calculator, and who needs it?
Your body loses water all day through sweat, urine and even breathing, and it needs to be replaced. This calculator estimates how much water you should aim to drink daily, in litres and in standard 250 ml glasses, based on your body weight and how long you exercise.
It is useful for office workers who forget to drink while at their desk, people who walk, run, cycle or play sports, and anyone living in a hot, humid city. It also helps if you want to build a habit, such as finishing a one-litre bottle three times a day. To see whether your weight is in a healthy range, try our BMI Calculator.
Formula used
- Base water (litres) = body weight in kg × 0.033
- Exercise water (litres) = (exercise minutes ÷ 30) × 0.35
- Total daily water = base water + exercise water
- Glasses = total litres ÷ 0.25, rounded to the nearest whole number
The 33 ml per kg figure is a widely used rule of thumb, not an official standard.
Worked example
Take a person who weighs 70 kg and exercises for 30 minutes a day. Base water = 70 × 0.033 = 2.31 litres. Exercise water = (30 ÷ 30) × 0.35 = 0.35 litres. Total = 2.66 litres, which the calculator shows as 2.7 L. In glasses, 2.66 ÷ 0.25 = 10.64, so about 11 glasses.
Now compare a 55 kg person who does not exercise: 55 × 0.033 = 1.815 litres, shown as 1.8 L, or about 7 glasses. An 80 kg person who exercises for 60 minutes needs 80 × 0.033 = 2.64 litres plus (60 ÷ 30) × 0.35 = 0.70 litres, a total of 3.34 litres (3.3 L), or about 13 glasses.
Frequently asked questions
How much water should I drink in a day?
It depends on your body size, activity, weather and health. This calculator uses a common rule of thumb of about 33 ml per kg of body weight, plus 0.35 litres for every 30 minutes of exercise. Treat the result as a starting point, not a medical target.
Do tea, coffee, chaas and food count towards my water intake?
Most of the fluid in tea, coffee, buttermilk, coconut water and soups counts towards your daily total, and so does the water in foods such as fruit, vegetables and dal. Plain water is still the best main source, especially if you take a lot of sugary drinks.
Should I drink more water in summer or humid weather?
Usually yes. In hot or humid weather you lose more water through sweat, so you may need more than the calculator shows. Drink steadily through the day and watch your urine colour: pale yellow is a good sign, and dark yellow suggests you need more fluids.
Can you drink too much water?
Yes, though it is uncommon. Drinking a very large amount in a short time can dilute the sodium in your blood, a condition called hyponatraemia. Spread your water across the day and do not force yourself to drink far beyond your thirst unless a doctor has told you to.
Why does the result differ from the 8 glasses a day rule?
The 8 glasses rule is a popular rule of thumb that gives everyone the same number. This calculator adjusts for body weight and exercise, so a heavier or more active person gets a higher figure and a lighter, less active person gets a lower one.
Limitations and accuracy
This is a general estimate for a healthy adult, not a prescription. It does not account for climate, altitude, age, pregnancy, breastfeeding, illness, fever, or how much fluid you already get from food and other drinks. Some conditions, such as kidney disease, heart failure or liver problems, may require you to limit fluids, so follow your doctor's advice if you have one of these. If you are unsure, use the result as a guide, listen to your thirst and check with a doctor or dietitian. This tool is for information only and is not medical advice.