Daily Water Intake Calculator
Get a daily water target from your weight and exercise, in ounces, liters, cups and bottles.
- Free
- No sign-up
- Runs in your browser
- Shows the math
Enter your weight to see your number.
Weight in kg × 32.5 mL + 0.6 L per hour of exercise
General information, not medical advice. Medical disclaimer
Why your number may differ from 64 oz or 8 glasses
Eight 8-ounce glasses is 64 oz, and a review of the research found no scientific studies behind that rule. Your number here comes from your weight and your exercise, so it moves when you do. For a lot of adults it lands above 64 oz, and a few land below it. Is 64 oz of water a day enough? goes through where the rule came from.
| Group | Total, liters | Total, fl oz | Drinks, liters | Drinks, fl oz |
|---|---|---|---|---|
| Women | 2.7 | 91 | 2.2 | 74 |
| Men | 3.7 | 125 | 3.0 | 101 |
Worked example: 160 lb, 30 minutes, typical weather
- 160 lb is 72.57 kg (160 divided by 2.2046).
- 72.57 kg × 32.5 mL = 2,359 mL for body weight.
- 30 minutes is 0.5 hour, and 0.5 × 600 mL = 300 mL for exercise.
- 2,359 + 300 = 2,659 mL, which rounds to 2,650 mL.
- That's 90 fl oz, 2.65 liters, 11.2 cups, or 5.3 bottles of 500 mL. The likely range is 2,400 to 2,950 mL.
Press “Try an example” above to load it.
How the calculator works
- Weight sets the baseline. Your weight in kilograms times 32.5 mL, the middle of the common 30 to 35 mL per kg range.
- Exercise adds to it. 0.6 L for each hour of exercise, the middle of a 0.4 to 0.8 L per hour range. The ACSM position stand gives that range as a possible starting point for marathon runners. We use the middle of it for any kind of exercise, which is our own simplification.
- Heat moves you up the range. Hot or humid weather uses the top of both ranges.
- Food covers about a fifth. The result is a target for drinks. Total water including food is that number divided by 0.8.
The total is rounded to the nearest 50 mL, and every other unit is converted from that rounded number, so ounces, liters, cups and bottles always agree.
Some of this is a rule of thumb and some is a published figure. The 30 to 35 mL per kg range is a common rule of thumb, and we didn't find a formal guideline for it. The 80/20 split between drinks and food comes from the National Academies, and the exercise add-on uses the middle of the 0.4 to 0.8 L per hour starting range that the ACSM position stand gives for marathon runners, applied to all exercise as our simplification. The same position stand says sweat rates vary a lot and recommends weighing yourself before and after exercise, which is what the sweat rate calculator does. Our own check: the weight rule lands within about 50 mL of the National Academies drink figures at 147 lb and 201 lb. The full method is on Water intake formulas compared.
When this number does not apply
- You're pregnant or breastfeeding.
- You have a kidney, heart or liver condition.
- You have been given a fluid limit or a specific drinking target.
- You take a medication that affects fluids or sodium.
- This is for a child or teen. The calculator is for adults.
More water calculators
- Bottles of Water per Day CalculatorTurn a daily goal into bottles and drink-by times.
- How Many Bottles of Water Are in a Gallon?Convert gallons, liters or ounces into any bottle size.
- Creatine Water Intake CalculatorA water number for maintenance or loading, with what the research found.
- Sweat Rate CalculatorWeigh yourself before and after a workout to find liters per hour.
- Water Intake Calculator for Weight LossA daily target plus the before-meal plan used in two trials.
- Pregnancy Water Intake CalculatorThe National Academies figures for pregnancy and breastfeeding.
- All Water CalculatorsEvery calculator on one page.
Guides
- Water Intake by WeightA chart from 100 to 250 lb, with ounces, liters and cups.
- Water Intake Formulas ComparedHalf your body weight, 35 mL per kg and the National Academies side by side.
- What Counts as Water IntakeCoffee, tea, sparkling water and food.
- Is 64 oz of Water a Day Enough?Where the 8 glasses rule came from and what fits your size.
- How Much Water Is Too Much?How overhydration happens, who is at risk, and when to see a doctor.
- Is a Gallon of Water a Day Too Much?Who a gallon fits, who it does not, and why speed matters.
- Does Creatine Make You Retain Water?What the research says about early weight gain.
- Do You Need Electrolytes?When plain water is enough and when electrolytes may help.
- Why Do I Pee So Much When I Drink Water?The usual reason, other causes, and warning signs.
- All Hydration GuidesEvery guide on one page, grouped by question.
Frequently asked questions
Why does my number differ from 8 glasses or 64 oz?
Eight 8-ounce glasses adds up to 64 oz, a round number. A review in the American Journal of Physiology went looking for the research behind it and found no scientific studies in support of “8 x 8”. This calculator starts from your weight and adds your exercise, so larger or more active adults will usually land above 64 oz. See Is 64 oz of water a day enough?
Does coffee or tea count?
For most healthy adults, yes. The National Academies count beverages, including caffeinated ones, toward total water, and Mayo Clinic lists tea, coffee and milk as drinks that count. Controlled studies found moderate coffee and tea hydrated about as well as water. The details, and the exceptions, are on What counts as water intake.
Do I count food?
Not for this number. It's a target for drinks. The National Academies and Mayo Clinic both say food supplies about 20% of your total water, and the “total water” line in the result adds that back in.
How do I know I am drinking enough?
Mayo Clinic says you're probably drinking enough if you rarely feel thirsty and your urine is colorless or light yellow. It lists headaches, dark urine and lower physical performance as signs you may be falling short. Use the calculator for a starting number and your own signs to adjust.
Can I drink too much?
Yes. The 2015 consensus statement on exercise-associated hyponatremia ties it to drinking more than you lose. That's why the exercise add-on here is a range and a starting point, not a schedule to force. If you have a fluid limit from your care team, follow that instead of this page.
Why is there no age or sex input?
They don't change the formula. The National Academies publish different totals for women and men. At 147 lb and 201 lb the weight-based rule lands within about 50 mL of their drink figures, 2.2 liters for women and 3.0 liters for men. Those aren't average weights. CDC data put average adult weight at about 172 lb for women and 199 lb for men, so a typical woman will land above the 2.2 liter reference. Fewer inputs also means more people finish. The calculator is for adults.
Why does heat change the result?
In hot or humid weather the calculator uses the top of both ranges, 35 mL per kg and 0.8 L per hour of exercise. The National Academies note that people who are very active or live in hot climates may need more water than the reference amounts.
What if I am pregnant or have a medical condition?
This calculator is for healthy adults and doesn't give numbers for pregnancy or breastfeeding. Mayo Clinic says pregnant or breastfeeding women may need more fluids, and some conditions call for less. The Pregnancy Water Intake Calculator shows the National Academies figures for both. Ask your own clinician for a number that fits you.
Sources
- National Academies of Sciences, Engineering, and Medicine. News release, Feb. 11, 2004. Report sets dietary intake levels for water, salt, and potassium to maintain health and reduce chronic disease risk.
- National Academies Press. Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate, 2005. Water chapter.
- Mayo Clinic. Water: How much should you drink every day?
- Sawka MN, Burke LM, Eichner ER, Maughan RJ, Montain SJ, Stachenfeld NS. American College of Sports Medicine position stand. Exercise and fluid replacement. Medicine & Science in Sports & Exercise 39(2):377-390. PubMed 17277604.
- Hew-Butler T, Rosner MH, Fowkes-Godek S, et al. Statement of the 3rd International Exercise-Associated Hyponatremia Consensus Development Conference, Carlsbad, California, 2015. British Journal of Sports Medicine 49(22):1432-1446. PubMed 26227507, DOI 10.1136/bjsports-2015-095004.
- Valtin H. “Drink at least eight glasses of water a day.” Really? Is there scientific evidence for “8 x 8”? American Journal of Physiology, Regulatory, Integrative and Comparative Physiology 283(5):R993-R1004. PubMed 12376390.
- NIST Special Publication 811, Appendix B.8. Factors for units listed by kind of quantity or field of science (volume).
- Centers for Disease Control and Prevention, National Center for Health Statistics. Body Measurements (mean weight of adults 20 and over, August 2021 to August 2023).
How this page was built. The Daily Water Intake Calculator on Daily Water Calculator was built by Cedrick Reese. The formulas run as plain code in your browser, and we checked them against hand-worked examples, including the 160 lb example on this page. The 80/20 split of drinks and food is from the National Academies, the exercise add-on is the middle of the ACSM position stand's 0.4 to 0.8 L per hour starting range for marathon runners, applied to all exercise as our simplification (the same stand says sweat rates vary and recommends weighing yourself), and the 30 to 35 mL per kg range is a rule of thumb that we cross-checked against the National Academies drink figures. When a source changes, we update the numbers and the sources list together. Last reviewed: .
General information for healthy adults, not medical advice. If you are pregnant or breastfeeding, or you have kidney, heart or liver conditions or a fluid limit, ask a clinician first. Terms and medical disclaimer.