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Daily Water Intake Calculator

This calculator estimates how much water you should drink each day based on your body weight and physical activity level, giving results in liters, milliliters, and fluid ounces.

Recommended Daily Water Intake
2.45 L/ 82.8 fl oz
2,450
milliliters
2.45
liters
10.4
8 fl oz glasses

Based on 70 kg body weight with sedentary activity. Includes fluids from beverages only — food contributes an additional ~20% of daily fluid needs.

Quick answer

Most adults need approximately 35 mL of water per kilogram of body weight per day as a baseline. A 70 kg sedentary person needs about 2.45 liters (82 fl oz) daily, while a moderately active 80 kg person needs roughly 3.3 liters (112 fl oz). Physical activity, climate, and health conditions all increase water needs. These estimates align with guidelines from the National Academies of Sciences and the European Food Safety Authority.

Formula & method

Water (mL) = Weight (kg) × 35 + Activity Addition (mL)
  • Weight (kg) — Body weight in kilograms
  • 35 mL/kg — Standard hydration baseline per kilogram of body weight
  • Activity Addition — Extra mL added based on daily physical activity level

Baseline of 35 mL per kg of body weight, adjusted upward by activity level. Activity additions: sedentary = 0 mL, light = 300 mL, moderate = 500 mL, intense = 1000 mL.

Water (oz) = Weight (lb) × 0.5 + Activity Addition (oz)
  • Weight (lb) — Body weight in pounds
  • 0.5 oz/lb — Standard half-ounce per pound hydration rule
  • Activity Addition — Extra ounces added for physical activity

Imperial equivalent: half an ounce per pound of body weight as the baseline. Activity additions: sedentary = 0 oz, light = 10 oz, moderate = 17 oz, intense = 34 oz.

Examples

Example 1: Sedentary woman, 60 kg
Input
Weight: 60 kg, Activity: Sedentary
Result
2,100 mL (2.10 L / 71.0 fl oz)
Why
60 kg × 35 mL/kg = 2,100 mL baseline. No activity addition for sedentary. Final recommendation: 2,100 mL = 2.10 L = 71.0 fl oz per day.
Example 2: Lightly active man, 75 kg
Input
Weight: 75 kg, Activity: Light (1–3 days/week)
Result
2,925 mL (2.93 L / 98.9 fl oz)
Why
75 kg × 35 mL/kg = 2,625 mL baseline. Light activity adds 300 mL. Total: 2,625 + 300 = 2,925 mL = 2.93 L = 98.9 fl oz per day.
Example 3: Moderately active man, 85 kg
Input
Weight: 85 kg, Activity: Moderate (3–5 days/week)
Result
3,475 mL (3.48 L / 117.5 fl oz)
Why
85 kg × 35 mL/kg = 2,975 mL baseline. Moderate activity adds 500 mL. Total: 2,975 + 500 = 3,475 mL = 3.48 L = 117.5 fl oz per day.
Example 4: Sedentary adult, 150 lb (imperial)
Input
Weight: 150 lb, Activity: Sedentary
Result
75.0 fl oz (2,218 mL / 2.22 L)
Why
150 lb × 0.5 oz/lb = 75.0 fl oz baseline. No activity addition for sedentary. Converting: 75.0 fl oz × 29.5735 mL/oz = 2,218 mL = 2.22 L per day.

Frequently asked questions

Does the 8 glasses a day rule hold up scientifically?

The '8 × 8' rule (eight 8-oz glasses = 64 fl oz/1.9 L) is a popular heuristic but lacks strong scientific backing as a universal target. The National Academies set adequate intake at 3.7 L/day for men and 2.7 L/day for women from all sources (including food, which contributes about 20%). Body weight and activity are better personalizers than a fixed number.

Should I count coffee, tea, and other beverages toward my water intake?

Yes. Coffee, tea, milk, juice, and other beverages all contribute to daily fluid intake. Even caffeinated drinks count — research shows that moderate caffeine consumption does not cause net dehydration in regular drinkers. Alcohol is the main exception; it has a diuretic effect and should not be counted toward your target.

How does hot weather or sweating affect my water needs?

Heat and sweating significantly increase water needs. Exercising in hot conditions can raise fluid requirements by 500–2,000 mL per hour of activity. If you live in a hot climate, are pregnant, breastfeeding, or have a fever, add 500–1,000 mL above your calculator result as a starting point and adjust based on thirst and urine color.

What is the best way to tell if I am drinking enough water?

Urine color is the simplest field test: pale yellow (like lemonade) indicates good hydration, while dark yellow or amber suggests you need more water. Feeling thirsty, having a dry mouth, or experiencing fatigue or headaches are early signs of mild dehydration. Clear, nearly colorless urine all day can indicate over-hydration, which dilutes electrolytes.

Can you drink too much water?

Yes, drinking far more water than the kidneys can process (roughly more than 0.8–1.0 L per hour for extended periods) can cause hyponatremia, a dangerous drop in blood sodium. In practice this is rare except during endurance events. For healthy people following this calculator's recommendations, over-hydration is not a concern.

Do children and older adults have different water needs?

Yes. Children have higher water needs relative to body weight than adults, especially during growth and physical activity. Older adults often experience a reduced thirst sensation and need to drink proactively even without feeling thirsty, as dehydration risk increases with age. This calculator is calibrated for healthy adults; consult a pediatrician for children's targets.

Sources & references

External references open in a new tab. We are independent and not affiliated with these organizations.

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Provided “as is” for general information only — results may be inaccurate, so verify before you rely on them. No warranty; use at your own risk.

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