How to Calculate Water Intake
What is Water Intake?
A water intake calculator estimates your daily hydration needs based on body weight and activity level. The general guideline is 35ml per kg of body weight, adjusted upward for exercise and heat.
Formula
liters_per_day = body_weight_kg × 0.033; or fl_oz = weight_lbs / 2
- kg
- Body weight (kg) — Current body weight in kilogrammes
- L
- Water per day (L) — Recommended daily water intake
- lbs
- Body weight (lbs) — Current body weight in pounds
Step-by-Step Guide
- 1Base intake = body weight (kg) × 35 ml
- 2Sedentary adjustment: ×1.0, Moderate: ×1.15, Active: ×1.35
- 3Add 500ml per 30 minutes of intense exercise
- 4~20% of daily water comes from food
Worked Examples
Input
70kg person, moderate activity
Result
~2.8 litres/day (11.2 glasses)
Input
90kg active athlete
Result
~4.25 litres/day
Input
55kg sedentary person
Result
~1.9 litres/day
Frequently Asked Questions
How much water should I drink daily?
General rule: 33 ml per kg of body weight. For 70 kg person: 2.3 L (roughly 8–10 cups). Varies by activity, climate, health.
Is there a simple rule?
Yes: drink half your body weight in ounces. 150 lbs → 75 fl oz/day (~2.2 L). Add more for exercise, hot climates.
Can I drink too much water?
Rare but possible (hyponatremia). Normal intake is safe. Listen to thirst, increase intake during exercise/heat.
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