How Much Water Per Day by Body Weight: The mL-per-kg Formula and Adjustments
October 21, 2026
There is no single correct amount of water for everyone, but a body-weight formula gives a useful starting point. Many clinical references suggest around 30 to 35 milliliters of fluid per kilogram of body weight per day for healthy adults. For a 70 kg person, that is 2.1 to 2.45 liters. This figure is an estimate of total fluid from drinks, and you can adjust it for activity, climate, and health status.
The old rule of eight glasses a day (about 1.9 liters) falls in the same region, but body size matters: a 100 kg person needs more than a 50 kg person.
Skip the math and get your answer instantly:
Open the Water Intake Calculator →The Basic Calculation
Multiply your weight in kilograms by 30 to 35 mL. For 60 kg: 1,800 to 2,100 mL. For 70 kg: 2,100 to 2,450 mL. For 80 kg: 2,400 to 2,800 mL. To work in ounces, a common approximation is half your weight in pounds, expressed in fluid ounces: a 160 lb person would drink about 80 fluid ounces (2.4 liters).
The US National Academies set adequate intake for total water, from all beverages and food, at about 3.7 liters per day for men and 2.7 liters for women. Roughly 20% of that comes from food, leaving about 3.0 liters of drinks for men and 2.2 liters for women on average.
| Body weight | 30 mL per kg | 35 mL per kg |
|---|---|---|
| 50 kg | 1.50 L | 1.75 L |
| 60 kg | 1.80 L | 2.10 L |
| 70 kg | 2.10 L | 2.45 L |
| 80 kg | 2.40 L | 2.80 L |
| 90 kg | 2.70 L | 3.15 L |
What Counts Toward Your Intake
All beverages count, including tea, coffee, milk, and juice. Caffeinated drinks have only a mild diuretic effect in regular consumers and still contribute to hydration. Water-rich foods such as fruit, vegetables, soup, and yogurt supply a meaningful share. Alcohol is dehydrating at higher doses and should not be counted as fluid.
Plain water is the best default because it has no calories or added sugar, but variety helps people drink enough.
Adjusting for Exercise, Heat, and Health
Add 400 to 800 mL per hour of moderate exercise, more in hot conditions. You can measure your own sweat rate by weighing yourself before and after a session. Hot weather, high altitude, fever, vomiting, and diarrhea raise fluid needs. Pregnancy and breastfeeding also increase requirements.
People with heart failure, kidney disease, or certain medications may be told to limit fluids, so follow medical advice over any formula.
Signs of Getting It Wrong
Dark yellow urine, a dry mouth, headache, fatigue, and reduced urination suggest too little. Pale straw-colored urine is a practical sign of adequate hydration for most people. Drinking very large amounts quickly, especially during long endurance events, can dilute blood sodium and cause hyponatremia, so do not force fluids beyond thirst and the guidelines above.
Thirst is a reasonable guide for healthy adults, though older adults may have a blunted thirst response and benefit from scheduled drinks.
Making It Easy
Start the day with a glass, keep a bottle in view, drink with meals, and tie habits to cues such as coffee breaks. A 750 mL bottle refilled three times covers about 2.25 liters. Use a tracker only if it helps, because overthinking hydration often adds stress without benefit.
Frequently Asked Questions
How much water should I drink based on weight?
About 30 to 35 mL per kg of body weight per day, which is 2.1 to 2.45 liters for a 70 kg adult.
Does coffee count toward water intake?
Yes. For regular consumers, caffeinated drinks contribute to daily fluid intake.
Can I drink too much water?
Yes, though it is rare. Excessive intake in a short time can lower blood sodium to dangerous levels.
How do I know if I'm hydrated?
Pale yellow urine, regular urination, and absence of thirst are good practical signs.
Do I need more water when I exercise?
Yes, roughly 400 to 800 mL per hour of moderate exercise, more in heat.