Daily Water Intake Calculator
Estimate how much water to drink per day from body weight, exercise, and climate, in ml, ounces, cups, and liters. Based on common clinical guidance. Runs in your browser.
Estimated daily water
- Daily water (ml)
- 2660 ml
- Daily water (fl oz)
- 90 oz
- Daily water (8-oz cups)
- 11.2 cups
- Daily water (liters)
- 2.66 L
Estimate from ~33 ml/kg baseline, +~350 ml (12 oz) per 30 min of exercise, +10% in hot climates. Food provides ~20% of intake on top of this. The U.S. National Academies set adequate total water intake at ~3.7 L (men) and ~2.7 L (women) from all sources. Needs vary widely — thirst and pale-yellow urine are good guides. Not medical advice.
About this tool
There is no single right number for water intake, but body weight, activity, and climate give a sensible starting estimate, and that is what this calculator produces. It uses a common clinical rule of thumb of about 33 ml of water per kilogram of body weight as a baseline, adds roughly 350 ml (12 oz) for every 30 minutes of exercise to replace sweat losses, and increases the total by about 10% for hot or humid conditions. The result is shown in milliliters, fluid ounces, 8-ounce cups, and liters. Two things to keep in perspective: food contributes roughly 20% of daily water on top of what you drink, and the U.S. National Academies set adequate total intake (from all sources) at about 3.7 liters for men and 2.7 liters for women — so this drinking estimate sits below those all-source figures by design. Individual needs vary widely with sweat rate, diet, and health, and your body's own signals — thirst and pale-yellow urine — are reliable everyday guides. It is informational, not medical advice.
How to use it
- Enter your body weight.
- Enter your typical daily exercise in minutes.
- Choose temperate or hot/humid climate.
- Use the estimate as a target, and adjust to thirst and urine color.
Frequently asked questions
- Is the "8 glasses a day" rule accurate?
- It is a rough heuristic, not a scientific requirement. Needs scale with body size, activity, and climate, which is why this calculator personalizes the estimate. Eight 8-oz cups (about 1.9 L) is in the right ballpark for an average sedentary adult but too low for many active people.
- How is the baseline calculated?
- About 33 ml per kilogram of body weight per day — the midpoint of the commonly cited 30–35 ml/kg clinical range. A 70 kg person gets a ~2.3 L baseline before adding exercise and climate adjustments.
- How much extra should I drink when exercising?
- Roughly 350 ml (12 oz) per 30 minutes of activity to offset sweat, more in heat or for heavy sweaters. For long or intense sessions, electrolytes matter too, not just water. The tool adds this on top of baseline.
- Does food count toward hydration?
- Yes — food typically provides about 20% of total water intake (fruits, vegetables, soups). This calculator estimates water to drink; the all-source totals from the National Academies (3.7 L men, 2.7 L women) include food and other beverages.
- Can I drink too much water?
- Rarely, but yes — excessive intake in a short time can cause hyponatremia (dangerously low blood sodium), a risk mainly for endurance athletes over-drinking plain water. Spread intake through the day and include electrolytes during prolonged exercise.
- Is this medical advice?
- No. It is a general estimate. People with heart, kidney, or liver conditions, or who are pregnant, should follow individualized medical guidance on fluid intake.