Daily drinking-water planning — not a prescription
Water Intake Calculator
A common planning rule is half your body weight in pounds as fluid ounces per day, then add roughly 12 ounces for every 30 minutes of exercise. A 160 lb person with 30 minutes of exercise needs about 92 ounces (2.7 L). Adjust for heat and thirst; this is not medical advice.
Suggested daily water
92 fl oz
- Cups (8 fl oz)
- 11.5 cups
- Milliliters
- 2,721 mL
- Liters
- 2.72 L
- Base from body weight
- 80 fl oz
- Extra for activity / heat
- 12 fl oz
When this estimate helps
- Setting a bottle target for a normal workday
- Scaling intake up on long training days without guessing
- Translating a kg body weight into a US-ounce bottle plan
- Explaining the half-body-weight rule to someone new to it
Limits of this estimate
- Treating the number as medical advice during illness, pregnancy or kidney disease
- Chugging the full amount at once instead of spreading fluids through the day
- Ignoring food moisture and then overshooting plain water
- Using the hot-weather bonus and still skipping electrolytes on heavy sweat days
How this water intake estimate works
- Convert body weight to pounds if needed (1 kg ≈ 2.205 lb).
- Base intake (fl oz) = body weight in pounds × 0.5.
- Activity bonus = (exercise minutes ÷ 30) × 12 fl oz.
- Hot or humid climate adds 16 fl oz. Cold climate adds nothing in this model.
- Total ounces = base + activity + climate. Convert: cups = oz ÷ 8; mL = oz × 29.5735.
Needs vary with age, pregnancy, illness, diet and medications. Follow a clinician’s guidance if you have a medical condition.
Worked examples
Desk day, no workout
70 kg adult, no exercise, moderate climate.
77 fl oz · ≈ 9.6 cups
After a one-hour run
160 lb runner, 60 minutes exercise, moderate climate.
3.08 L · ≈ 104 fl oz
Hot weather outdoor work
180 lb person, 90 minutes activity, hot climate.
142 fl oz · ≈ 17.8 cups
Frequently asked questions
Is half your body weight in ounces a medical standard?
No. It is a widely shared planning heuristic. Official dietary reference intakes discuss total water from drinks and food together and vary by age and sex. Use this page as a starting point, not a prescription.
Does coffee or tea count?
Many people count most non-alcoholic fluids toward daily intake. Very high caffeine or alcohol can still dehydrate relative to plain water for some people—use judgment.
Should I drink this all at once?
No. Spread fluids through the day. Large boluses are harder to absorb and can be uncomfortable.
Why add water for exercise?
You lose fluid in sweat. The 12 oz per 30 minutes figure is a simple average; heavy sweaters in heat may need more, and short easy walks may need less.
Sources and updates
Last reviewed . Heuristic model; not individualized medical guidance.
- Half-body-weight ounces heuristic – Common consumer planning rule (oz ≈ body weight lb × 0.5). Not an official clinical standard.
- NIST – Unit conversion – Pound/kilogram and fluid ounce conversion factors.
For general education only. Not medical advice. People with kidney, heart or endocrine conditions should follow a clinician’s fluid recommendations.