Water Intake Calculator: How Much Water You Need Per Day
A water intake calculator starts from the National Academies adequate intake: about 3.7 liters of total water a day for men and 2.7 liters for women, counting all beverages and food.[1] About 80% comes from drinks, roughly 3.0 L and 2.2 L. Body-weight formulas are unsourced rules of thumb, not the reference standard, and the tool below labels them that way.
Water intake calculator
Reference values, not a personal target. They count water from food and drinks, and needs change with health, climate, and medicines.
How much water should you drink per day?
The reference figures are for total water, which means everything from drinks and food together. In a 2004 report, the Institute of Medicine, now part of the National Academies, set adequate intakes of about 3.7 liters (125 ounces) of total water a day for men and about 2.7 liters (91 ounces) for women.[1] About 80% of people's total water comes from drinking water and other beverages.[1] Eighty percent of 3.7 L is 2.96 L, or about 100 fl oz, and 80% of 2.7 L is 2.16 L, or about 73 fl oz. Those are arithmetic on the published share, not separate published targets. The full report, Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate, lists adequate intakes of total water from drinking water, beverages, and food.[2] The calculator shows the reference value for the sex you choose, then the drink share beside it, in liters and in US fluid ounces.
| Group | Total water | From drinks (about 80%) | From food (about 20%) |
|---|---|---|---|
| Men | 3.7 L (125 fl oz) | 2.96 L (100 fl oz) | 0.74 L (25 fl oz) |
| Women | 2.7 L (91 fl oz) | 2.16 L (73 fl oz) | 0.54 L (18 fl oz) |
Does water from food and other drinks count toward your intake?
Yes. The National Academies figures cover total water, so food and every kind of drink count. The release that announced them says about 80% of total water comes from drinking water and beverages, which leaves about 20% from food.[1] For a woman at the 2.7 L reference value, that is about 0.54 L from food and 2.16 L from drinks. Soups, fruit, and vegetables all carry water. The same release says caffeinated beverages can contribute as much as noncaffeinated options, so coffee and tea are not subtracted from the total.[1] This is why a glass count can mislead. If someone drinks 2 L of fluid a day and also eats meals, their total water intake is higher than 2 L. The calculator reports the drink share separately for that reason. For a man at the 3.7 L reference value, food supplies about 0.74 L and drinks about 2.96 L.
Is the 8 glasses a day rule correct?
Not exactly: it is a rounded simplification, not a National Academies figure. Eight glasses of 8 fluid ounces is 64 fl oz, which is about 1.9 liters. That is below the 2.96 L drink share for men and 2.16 L for women worked out from the reference values, and it ignores water from food.[1] The National Academies release points to thirst, not glass counts. It says people get adequate amounts of water from normal drinking behavior and by letting their thirst guide them.[1] Eight 8-ounce glasses is about 64% of the 2.96 L drink share for men and 88% of the 2.16 L share for women. Your own needs depend on your size, your food, the weather, and how active you are. The calculator gives you the reference value and the drink share, and it leaves the glass count out of the math.
Should water intake be based on body weight?
Not by the reference standard, because the National Academies adequate intakes are stated per day for men and women, not per kilogram of body weight.[1] Body-weight formulas, such as 30 to 35 mL per kg, are a rule of thumb without a primary source, and this page says so plainly. The tool shows that range separately, labeled unsourced, only if you enter a weight. At 80 kg it gives 2.4 to 2.8 L, and at 60 kg it gives 1.8 to 2.1 L. Compare 2.4 to 2.8 L with the 2.96 L drink share for men. They are close, but they are not the same measure: one is a convention about intake, the other is the drink part of a published adequate intake. If a formula and the reference value disagree, trust the reference value, and ask a clinician if you have a health condition that affects fluids.
| Body weight | 30 mL per kg | 35 mL per kg |
|---|---|---|
| 50 kg | 1.5 L | 1.75 L |
| 60 kg | 1.8 L | 2.1 L |
| 70 kg | 2.1 L | 2.45 L |
| 80 kg | 2.4 L | 2.8 L |
| 90 kg | 2.7 L | 3.15 L |
| 100 kg | 3.0 L | 3.5 L |
Who needs more water than the reference value?
Heat and effort raise needs. The National Academies release says very active individuals who are continually exposed to hot weather often have daily total water needs of six liters or more.[1] Six liters is about 203 fl oz, which is roughly 1.6 times the 3.7 L reference for men and 2.2 times the 2.7 L reference for women. The release also says the panel did not set an upper limit for water.[1] That is not advice to drink without limit. Some people need the opposite: those with heart or kidney conditions, or on a prescribed fluid limit, should follow their clinician and ignore any general calculator. The tool has a hot climate or heavy exercise checkbox that adds a note, and it shows no extra number, because no published figure converts your day into liters.
Does GLP-1 medication change how much water you need?
No liter target is published for GLP-1 medicines, so none is claimed here, but fluid loss is a documented concern. A 2025 joint advisory from four nutrition and obesity societies states that dehydration from severe nausea, vomiting, or diarrhea can cause acute kidney injury, and it lists ensuring adequate fluids among the habits to encourage.[3] The Ozempic label says the majority of reported acute kidney injury events occurred in patients with gastrointestinal reactions leading to dehydration such as nausea, vomiting, or diarrhea.[4] The Wegovy (semaglutide), Mounjaro and Zepbound (tirzepatide) labels carry matching warnings and tell prescribers to monitor kidney function when patients report reactions that could cause volume loss.[5][6][7] The advisory also reports 16% to 39% lower energy intake, which can mean less of the roughly 20% of water that comes with food.[3][1] If you have persistent vomiting or diarrhea, or you cannot keep fluids down, contact your prescriber instead of using a calculator.
Frequently asked questions
How many ounces is 2.7 liters?
2.7 liters is about 91 US fluid ounces, using 29.57 mL per fluid ounce. That is the National Academies adequate total water for women, counting food and drinks. The drink share is about 2.16 L, or 73 fl oz.
How much water should I drink on Ozempic, Wegovy, Mounjaro or Zepbound?
No liter target is published for these medicines. The 2025 joint advisory and the drug labels warn that dehydration from nausea, vomiting, or diarrhea can cause acute kidney injury. Staying hydrated is a question for your prescriber, especially if you cannot keep fluids down.
Do coffee and tea count toward water intake?
Yes. The National Academies release says caffeinated beverages can contribute as much as noncaffeinated options. Coffee and tea count as part of your drinks, which are about 80% of total water.
Is thirst a reliable guide to how much to drink?
For most healthy people, according to the National Academies release, which says people get adequate water from normal drinking behavior and by letting thirst guide them. Illness, heat, and some medicines can change that, so ask a clinician if unsure.
Can you drink too much water?
The National Academies panel did not set an upper limit for water. That does not make any amount safe for everyone. People with kidney or heart conditions, or a prescribed fluid limit, should follow their clinician instead.
Does PepTrac track water?
Yes. PepTrac for iPhone shows daily water progress with calories and protein. Amounts are stored in milliliters and shown in your preferred unit. PepTrac is free to download, with an optional PepTrac Pro, and it is not medical advice.
Is this water calculator medical advice?
No. It shows published reference intakes for healthy adults and an unsourced rule of thumb. Pregnancy, heart or kidney conditions, and prescribed fluid limits change needs, so follow your clinician instead of any calculator.
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 (news release, February 11, 2004). Accessed October 3, 2026.
- National Academies of Sciences, Engineering, and Medicine. Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate (2005). Accessed October 3, 2026.
- American College of Lifestyle Medicine, American Society for Nutrition, Obesity Medicine Association, The Obesity Society (Obesity, 2025). Nutritional priorities to support GLP-1 therapy for obesity: a joint advisory. Accessed October 3, 2026.
- DailyMed, National Library of Medicine (Novo Nordisk). Ozempic (semaglutide) injection prescribing information. Accessed October 3, 2026.
- DailyMed, National Library of Medicine (Novo Nordisk). Wegovy (semaglutide) prescribing information. Accessed October 3, 2026.
- DailyMed, National Library of Medicine (Eli Lilly). Mounjaro (tirzepatide) injection prescribing information. Accessed October 3, 2026.
- DailyMed, National Library of Medicine (Eli Lilly). Zepbound (tirzepatide) prescribing information. Accessed October 3, 2026.
Written and maintained by the team that builds PepTrac. Every calculator on this site runs the same tested math as the app. Read how we research, cite, and update pages in our editorial policy.
