How much water should I drink a day?

A common baseline is roughly half your body weight in ounces, adjusted up for activity and heat. National guidance from the National Academies suggests about 2.7 liters a day for women and 3.7 liters for men from all fluids and food combined. Thirst and pale-yellow urine are good everyday signals.

Does coffee or tea count toward my water?

Yes. Despite the old myth, the fluid in coffee and tea counts toward your total. Water is still the best default because it has no sugar or calories.

Why does fiber increase my water needs?

Fiber absorbs water to soften stool and move it through the gut. If you raise your fiber without raising your fluids, you can feel more constipated and bloated, so the two are worth increasing together.

Verified formulaLast reviewed July 2026

Water Intake Calculator

Estimate how much water to drink each day based on your body weight, activity, and climate.

Your details

Weight (lbs)

Activity level

Climate

Calculated live in your browser. Nothing is stored or sent anywhere.

Awaiting details

—

Fill in your details to see your result.

A mathematical estimate based on validated equations, for education only. It is not a diagnostic tool.

The science

Fiber and water work as a team, so the more fiber you eat, the more your daily fluid matters. This calculator gives a practical starting estimate for total water based on your body weight, how active you are, and whether you spend time in the heat. Your true needs vary from day to day, so treat this as a friendly baseline rather than a strict rule, and let thirst and the color of your urine guide you the rest of the way.

The formula

Body weight (lb) x 0.5 oz, adjusted for activity and climate

Sources

1
Harvard Health Publishing, How Much Water Should You Drink? (health.harvard.edu)
2
Harvard T.H. Chan School of Public Health, The Nutrition Source: Water (nutritionsource.hsph.harvard.edu)

Common questions

This tool is for education only and is not a diagnostic device. Consult a licensed clinician before making health decisions.