How the water intake is estimated

The calculator starts with your body weight and then adds extra water for the things that make you lose more fluid.

Daily water = weight × 33 mL per kg + exercise + climate + pregnancy or breastfeeding

| Part | Amount added | |---|---| | Body weight | 33 mL per kg (0.033 L), about 0.5 fl oz per lb | | Exercise | 350 mL (about 12 fl oz) for every 30 minutes | | Hot or humid climate | +500 mL | | Very hot climate or high altitude | +1,000 mL | | Pregnancy | +300 mL | | Breastfeeding | +700 mL |

Worked example

A 70 kg adult who exercises for 30 minutes a day in a temperate climate:

Body weight: 70 × 33 = 2,310 mL
Exercise: 30 ÷ 30 × 350 = 350 mL
Total = 2,660 mL, or about 2.7 liters, which is roughly 90 fl oz or 11 cups

Other benchmarks

For comparison, the US National Academies of Sciences set adequate total water intakes of about 3.7 liters a day for men and 2.7 liters a day for women, including water from food and all drinks. Food typically supplies around 20%, so about 3.0 L (men) and 2.2 L (women) are expected to come from beverages.

The adjustments for climate, pregnancy and breastfeeding are practical rules of thumb, not medical prescriptions. Treat the answer as a starting point and let your thirst and the colour of your urine guide you.

How to find your daily water intake

Choose your units and enter your body weight.
Add your exercise. Enter the total minutes you work out or play sport on a typical day.
Pick your climate. Choose hot or very hot if you live somewhere warm, humid or high up, or sweat a lot.
Select pregnancy or breastfeeding if it applies.
Read your target in liters or ounces, plus cups, 500 mL bottles and a rough amount per waking hour.

The target is for water and other drinks across the whole day, so tea, coffee, milk and juice all count. Sip steadily instead of drinking a lot at once.

If you have kidney, heart or liver disease, or take medicines that affect fluid balance, ask your doctor how much to drink, because this estimate is not suitable for you.

Frequently Asked Questions

How much water should I drink a day?

A common starting point is about 33 mL per kg of body weight, so a 70 kg adult needs around 2.3 liters before exercise or heat are added. The US National Academies suggest total water of about 3.7 L for men and 2.7 L for women, including the roughly 20% that comes from food.

How much water should I drink by weight?

Multiply your weight in kilograms by 0.033 to get liters, or take about half of your weight in pounds as ounces of water. A 150 lb person gets about 75 fl oz from the half-your-weight rule. This calculator uses the metric version and adds extra for exercise, heat and life stage.

How much extra water do I need when I exercise?

A widely used guideline is about 12 fl oz (350 mL) for every 30 minutes of exercise. You may need more for long, intense sessions or in the heat. Start drinking before you are thirsty and replace what you lose over the following hours.

How much water should I drink when pregnant or breastfeeding?

Pregnancy raises fluid needs slightly, and breastfeeding raises them more because of the milk you produce. The adequate total water intake is about 3.0 L a day in pregnancy and 3.8 L while breastfeeding, compared with 2.7 L for other women. This calculator adds 300 mL and 700 mL as a practical estimate.

Do coffee, tea and food count towards my water intake?

Yes. Coffee, tea, milk, juice and the water in fruit, vegetables and soups all contribute to your fluid intake. Plain water is still a good default because it has no calories or sugar.

Can you drink too much water?

Yes, though it is uncommon. Drinking far more than your body needs in a short time can dilute the sodium in your blood, a condition called hyponatremia. Spread your drinks through the day, and avoid forcing large amounts of water at once.

How do I know if I am drinking enough?

Pale yellow urine, rarely feeling thirsty and passing urine several times a day are good signs. Dark urine, headaches, dry mouth or feeling dizzy can point to dehydration. Persistent symptoms are a reason to see a doctor.

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