Water Intake Calculator
This water intake calculator estimates how much water you should drink each day based on your body weight and activity level. It runs instantly in your browser and shows the result in ounces, liters, and glasses.
How much water should I drink?
How the water intake calculator works
A common rule of thumb is to drink about half your body weight in pounds as ounces of water each day. This water intake calculator starts from that baseline - roughly 0.5 ounces per pound - then adds extra for activity, since exercise and heat raise how much fluid you lose through sweat.
Estimates for general information only; not medical, nutrition, or fitness advice. Individual needs vary - consult a doctor or registered dietitian for personal guidance.
A worked example
Take a 150-pound adult. Half of 150 is 75, so the baseline is about 75 ounces, or a little over 2 liters, per day. Add a light workout and the calculator nudges that up by around 16 ounces; a longer, sweatier session pushes it toward 107 ounces. Hot, humid weather and higher altitude increase needs further, while a cooler, sedentary day trends toward the baseline.
These numbers include all fluids, not just plain water. Coffee, tea, milk, and the water in fruits and vegetables all count toward the total, so you rarely need to hit the figure with a glass in hand alone.
Using the water intake calculator wisely
Thirst and urine color are the simplest day-to-day guides: pale-yellow urine usually means you are well hydrated, while darker shades suggest you should drink more. Certain conditions - pregnancy, breastfeeding, kidney issues, or heart conditions - change fluid needs, sometimes requiring more and sometimes less, so treat the calculator as a starting point rather than a target to force.
The U.S. National Academies of Sciences and health agencies such as the Centers for Disease Control and Prevention note that most healthy people can let thirst guide them, and the OSHA heat-safety guidance stresses drinking more during hot or heavy work. If you have a medical condition affecting fluid balance, ask your doctor for a personal target.
Frequently asked questions
How much water should I drink a day?
A common baseline is about half your body weight in pounds, expressed as ounces - so around 75 ounces (2.2 liters) for a 150-pound adult - with more added for exercise, heat, pregnancy, or breastfeeding.
Does coffee or tea count toward water intake?
Yes. The water in coffee, tea, milk, juice, and foods like fruit and soup all counts toward your daily fluid total. Moderate caffeine has only a mild diuretic effect and still hydrates on balance.
Can I drink too much water?
Rarely, but yes. Drinking very large amounts in a short time can dilute blood sodium, a condition called hyponatremia. Spreading fluids through the day and following thirst avoids this for most people.
Should I drink more when exercising?
Yes. You lose water through sweat, so add fluid before, during, and after exercise. A rough guide is an extra 12 to 24 ounces per hour of activity, more in hot conditions.
Is the 8 glasses a day rule accurate?
Eight 8-ounce glasses (64 oz) is an easy-to-remember guide but not a strict rule. Actual needs depend on body size, activity, and climate, which is what this calculator estimates.
Balancing hydration with your fitness routine? Try our running pace calculator or the macro calculator to round out your plan.