Your details
For adults. This is WaterChamp’s starting estimate for drinks, not a clinical fluid requirement. The base rate and adjustment factors are app assumptions; the reference values below do not validate this exact formula.
1,800 ml of drinks per day
70 kg × 26 ml/kg = 1,820 ml, then × 1.00 sex × 1.00 age × 1.00 activity × 1.00 climate, plus 0 ml, rounded to the nearest 50 ml.
Fluid ounces are US fluid ounces (29.5735 ml). Glasses are 250 ml. “Per waking hour” spreads the total over 16 hours. Results change as you move the controls. Without JavaScript the page shows the 70 kg default.
What the result covers
The result is an estimate for drinks only. WaterChamp uses a base of 26 ml per kilogram to set a practical starting goal. Food also contributes water, but its share varies with diet; this formula does not measure that contribution.
Public-health reference values are totals for drinks plus food, so they run higher:
| Source | Women | Men | Includes food |
|---|---|---|---|
| EFSA, 2010[1] | 2.0 L/day | 2.5 L/day | Yes |
| U.S. National Academies, 2004[2] | 2.7 L/day | 3.7 L/day | Yes, about 80% arrives as drinks |
These are population reference values for healthy adults, not measurements of your personal requirement. This calculator scales with body weight instead: a 55 kg adult and a 110 kg adult do not get the same target.
Which inputs matter most
Weight and activity dominate. Moving from sedentary to very active multiplies the target by 1.5: for a 75 kg adult, 1,950 ml becomes 2,950 ml.
- Climate: ×1.0 to ×1.3. WaterChamp’s settings increase the estimate for warmer conditions. The exact multipliers are app assumptions.
- Sex: ±5% and age: ±5%. These are simplified profile adjustments, not measurements of body composition or hydration.
- Pregnancy and breastfeeding: +300 to +1,000 ml. These are the app’s goal adjustments. Individual needs and any prescribed fluid limits take precedence.
The model does not account for illness, altitude, individual sweat losses or a prescribed fluid restriction. Its precise output should not be mistaken for a precise measurement.
Why height and BMI are not inputs
This calculator uses WaterChamp’s weight-based formula. Height and BMI do not enter that formula; their absence is a modeling choice, not proof that body composition is irrelevant.
For example, with the other settings at their defaults, 64 kg gives 1,650 ml and 90 kg gives 2,350 ml. These are examples of the calculation, not targets for every person at those weights.
Limitations
The result is a starting point, not a prescription, and it is not medical advice. Kidney disease, heart failure, diabetes, and some medicines change how much fluid is safe to drink. Sometimes the safe amount is less, not more. If you are in treatment for any of those, use your clinician's figure instead. Too much water is not harmless either. Litres of plain water, taken faster than the kidneys can clear them, dilute blood sodium. That is dangerous.
Use any fluid target given by your clinician instead of this estimate. Changes in thirst or urine color are not a diagnosis and do not validate the calculator’s output.
Common questions
Does this number include the water in food?
No. It is the app’s estimate for drinks. Water in food contributes to total intake, but this calculator does not estimate your meals or subtract a measured food contribution.
Do coffee and tea count toward the total?
Yes. The Beverage Hydration Index trial compared thirteen drinks against still water over four hours. Skimmed milk, full-fat milk and an oral rehydration solution held water in the body better than water did. Tea, coffee, cola, orange juice and a sports drink were not measurably different from water.[3]
How many glasses is that?
Divide the millilitre result by 250. The calculator does this for you and draws the glasses. A 2,000 ml target is eight glasses. With the Imperial switch on, the panel counts 8 fl oz cups instead.
Can I get the result in fluid ounces?
Yes. Use the Metric/Imperial switch on the calculator. The result panel always shows both millilitres and US fluid ounces, whichever unit leads.
Should I spread it through the day?
The hourly figure is just the daily estimate divided across 16 waking hours. It is a planning aid, not a required drinking schedule or a claim about how much water you will retain.
What about drinks other than water?
Read how the app counts black coffee, green tea, sports drinks and coconut water, or compare the full drink guide. For coffee and tea timing, try the caffeine cutoff calculator.
Track it in the app
A target only helps if you can see your progress against it. The WaterChamp app for iPhone and Android works out the same goal from the same six inputs. It then counts what you drink toward that goal. It has 102 drinks built in, each with its own hydration, caffeine, alcohol and calorie values. A glass of wine and a glass of water do not count the same. It also shows a live hydration level through the day and tracks caffeine as your body clears it. It keeps home and lock screen widgets up to date. It writes your water to Apple Health and Health Connect.
[1] EFSA Panel on Dietetic Products, Nutrition and Allergies. “Scientific Opinion on Dietary Reference Values for water.” EFSA Journal, 2010;8(3):1459. efsa.onlinelibrary.wiley.com
[2] Institute of Medicine (now the National Academy of Medicine). Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate. National Academies Press, 2004. nap.nationalacademies.org
[3] Maughan RJ, Watson P, Cordery PA, et al. “A randomized trial to assess the potential of different beverages to affect hydration status: development of a beverage hydration index.” American Journal of Clinical Nutrition, 2016;103(3):717-723. pubmed.ncbi.nlm.nih.gov/26702122
