How much water do you need a day?
A quick estimate based on the National Academies’ daily water guidance, adjusted for exercise and hot weather. No signup, and nothing you enter leaves your browser.
2.4 L
about 80 fl oz, or 10 cups, from drinks each day
- Total water, drinks + food3 L (100 fl oz)
- From drinks (about 80%)2.4 L
- 8-ounce cups10
- 16.9-ounce bottles4½
A general estimate for healthy adults, not medical advice. If you have kidney, heart or liver disease or have been told to limit fluids, follow your clinician’s advice instead.
How does this water calculator work?
It starts from the National Academies’ Adequate Intake for total water, the amount healthy, well-hydrated adults typically take in each day, and adds two simple adjustments.
| Step | What we use | Where it comes from |
|---|---|---|
| Daily baseline (total water) | 2.7 L women, 3.7 L men, 3.0 L pregnant, 3.8 L breastfeeding | National Academies Adequate Intakes |
| Share from drinks | About 80% of the total | National Academies: about 20% usually comes from food |
| Exercise | Adds 0.5 L for every hour | Our simple estimate. Sweat rates vary widely, which is why sports guidelines recommend individual plans. |
| Hot or humid weather | Adds 0.5 L | A rough rule of thumb. Heat raises fluid needs, but by very different amounts for different people. |
For the full story on hydration and your lymphatic system, the watery network that returns fluid from your tissues to your blood, read How Much Water Should You Drink a Day?
Why doesn’t it ask for my weight?
The National Academies set their water guidance by sex and life stage, not body weight. Rules such as drinking half your body weight in ounces are popular shortcuts, not part of that guidance. Larger and very active people often do need more, which is what thirst and the exercise and heat adjustments are for.
How do I know if I’m drinking enough?
For most healthy people, drinking when thirsty and having a drink with meals is enough, the National Academies found. Rarely feeling thirsty and passing pale-yellow urine are good everyday signs. Dark urine, headaches or feeling dizzy in the heat are signs to drink more.
Can you drink too much water?
Yes, though it’s uncommon. Drinking far more than your body can get rid of, especially during long endurance events, can dilute the sodium in your blood, a condition called hyponatremia. More water than you need won’t make lymph move faster either. Steady drinking through the day, movement and deep breathing are the everyday basics.
Frequently asked questions
How much water should I drink a day?
Does coffee or tea count toward my water intake?
Why doesn’t the calculator ask for my weight?
Can you drink too much water?
Sources
- National Academies of Sciences, Engineering, and Medicine. “Report Sets Dietary Intake Levels for Water, Salt, and Potassium to Maintain Health and Reduce Chronic Disease Risk.” 2004. nationalacademies.org
- Institute of Medicine. Dietary Reference Intakes: The Essential Guide to Nutrient Requirements, “Water.” 2006. nap.edu
- Sawka MN, et al. “American College of Sports Medicine position stand. Exercise and fluid replacement.” Medicine & Science in Sports & Exercise, 2007. pubmed.ncbi.nlm.nih.gov
- Harvard T.H. Chan School of Public Health, The Nutrition Source. “Water.” nutritionsource.hsph.harvard.edu
- Centers for Disease Control and Prevention. “About Water and Healthy Drinks.” cdc.gov
- MedlinePlus. “Low blood sodium.” medlineplus.gov
Simple habits for healthy lymph flow
Water, movement, breathing and sleep do the everyday work. Our Journal explains each one in plain language, with sources.