Water Intake Calculator

Example Calculation

Someone who weighs 165 pounds and exercises 30 minutes a day in a mild climate gets half their body weight in ounces (82.5) plus 12 ounces for the workout: about 94.5 ounces a day. That is 2.8 liters, or about 12 eight-ounce glasses.

Remember that food and drinks like tea, milk and soup count toward this number. In very hot weather the calculator raises it by 10% to 20%.

How It Works

How much water you need depends on your body size, activity level and environment. This calculator uses a practical rule of thumb: about half an ounce of water per pound of body weight each day, plus roughly 12 ounces for every 30 minutes of exercise. A multiplier then adjusts the total for climate — more in hot or humid weather or at high altitude, a little less in cool conditions.

The result is shown in fluid ounces, liters, standard 8-ounce glasses and 16.9-ounce (500 mL) bottles, plus a per-hour target across a 16-hour waking day so you can spread your intake. Spreading water throughout the day is easier than trying to catch up in the evening.

For context, the National Academies of Sciences, Engineering, and Medicine has suggested total daily fluid intakes of about 125 ounces for men and 91 ounces for women from all beverages and foods. Roughly 20% of fluid intake typically comes from food, such as fruits, vegetables and soups. Coffee, tea and other beverages also contribute to hydration, despite common myths to the contrary.

Your needs can be higher if you have a fever, vomiting or diarrhea, are pregnant or breastfeeding, or take certain medications, and lower if you have kidney, heart or other conditions that require fluid limits. Pale yellow urine is a simple everyday sign of good hydration. When in doubt, follow the advice of your healthcare provider rather than a general-purpose calculator.

Formula Explained

Daily ounces = (weight in lb × 0.5 + exercise minutes ÷ 30 × 12) × climate factor

Liters = ounces × 0.0295735. Glasses = ounces ÷ 8.

Assumptions and limits

• This is a practical rule of thumb, not an official recommendation. The National Academies set an adequate total water intake of about 3.7 liters a day for men and 2.7 liters for women aged 19 to 30, from all drinks and food together.
• About 20% of total water usually comes from food, and other drinks also count. The number here is meant as a daily drinking target.
• Needs rise with illness, pregnancy, breastfeeding, fever and some medicines. Some conditions, such as kidney or heart disease, require limiting fluids, so ask your clinician.
• It is for healthy adults. It is not for children, and it is not advice for athletes in long events.