Daily Water Intake Calculator
Calculate how much water you should drink daily based on your weight and activity level.
Shows results in liters, ounces, and glasses.
Daily water intake needs vary based on body weight, physical activity, climate, and individual health conditions. The old “8 glasses a day” rule is an oversimplification — actual needs are highly personal.
Evidence-based baseline formula (National Academies, 2005):
Baseline Daily Water (oz) = Body Weight (lbs) × 0.5
Or equivalently: 35 mL per kg of body weight
Activity adjustment:
Add 12 oz (350 mL) per 30 minutes of moderate exercise
Climate adjustment:
- Hot/humid environment: add 16–24 oz
- High altitude (above 8,000 ft): add 16 oz
Worked example: A 170-lb person, exercises 45 minutes/day, lives in a warm climate:
- Baseline: 170 × 0.5 = 85 oz
- Exercise: (45/30) × 12 = 18 oz
- Climate: +16 oz
- Total: 119 oz ≈ 3.5 liters per day
Official intake recommendations (total from all sources including food):
| Group | Recommended Daily Total |
|---|---|
| Adult men | 3.7 L (125 oz) |
| Adult women | 2.7 L (91 oz) |
| Pregnant women | 3.0 L (101 oz) |
| Breastfeeding women | 3.8 L (128 oz) |
About 20% of daily water comes from food (especially fruits, vegetables, soups).
Signs of adequate hydration:
- Urine is pale yellow to clear
- Urinating 6–8 times per day
- No persistent dry mouth or headaches
Signs of dehydration (even mild):
- Dark yellow or amber urine
- Fatigue, difficulty concentrating
- Headache (often before thirst appears)
- Reduced physical performance after just 1–2% body weight fluid loss
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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