Water Intake Calculator: Daily Hydration by Weight, Activity & Temperature
Daily Water Intake Calculator
“Drink 2 liters of water a day” is a guideline most people have heard. But that number changes depending on your weight, activity level, and the temperature outside. A 65 kg desk worker and an 80 kg athlete have very different hydration needs.
Daily Water Intake Calculator
Hydration
Calculate your optimal daily water intake based on weight, activity level, and temperature.
Total Recommended
2600ml
11 cups (250ml each)
Calculation Formula
Base amount = Body weight (kg) × 30 ml
Activity bonus: Light exercise +350 ml / Heavy exercise or physical labor +700 ml
Temperature bonus: Warm (20–30°C) +150 ml / Hot (30°C+) +350 ml
Diuretic offset: 1 coffee +150 ml / 1 alcoholic drink +250 ml
Does coffee count against hydration? Caffeine has a mild diuretic effect. An Americano-sized cup of coffee prompts roughly 150 ml of additional fluid loss — so add that back into your target.
Signs of Dehydration
| Sign | Implication |
|---|---|
| Dark yellow urine | Early sign of insufficient fluids |
| Dry mouth and headache | Mild dehydration (−1–2% body water) |
| Dizziness and trouble concentrating | Moderate dehydration (−3–5%) |
| Severe fatigue and muscle cramps | Severe dehydration (rehydrate immediately) |
Optimal Drinking Schedule
| Time | Recommendation |
|---|---|
| Immediately after waking | 200 ml — replenish overnight fluid loss |
| 30 min before meals | 200 ml — promotes satiety, aids digestion |
| Mid-morning and mid-afternoon | 200 ml × 2–3 times |
| Before, during, and after exercise | 150–300 ml each |
| 1 hour before bed | ≤150 ml — avoid disrupting sleep with nocturia |
Drinking 200 ml at a time throughout the day absorbs better than downing 500 ml at once. Setting a reminder every 2 hours for a glass of water is the most effective habit-building approach.
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