Water Intake Calculator
Estimate daily water intake from body weight using the 30-35 mL/kg guideline. Adjust for exercise, climate and caffeine. Reference only, not medical advice.
Last updated: May 2026
Enter weight to estimate daily water intake.
Daily water intake: what the estimate means
The 30-35 mL per kg body weight guideline is a clinical approximation, not a precise target. A 75 kg person gets a baseline of 2,250-2,625 mL per day, adjusted upward for heat, exercise or illness. The calculator adds a fixed increment for the activity/heat selection: 350 mL for a warm or active day, 700 mL for very active or hot conditions.
About 20-30% of daily water intake comes from food, fruit and vegetables are 70-95% water by weight. A diet with substantial fresh produce can contribute 600-800 mL per day, meaning the calculated total does not all need to come from drinking. Thirst, urine colour (pale yellow = well hydrated), and kidney function are better real-time guides than a fixed daily target.
Daily water intake reference
| Body weight | Baseline (ml/day) | Active day (ml/day) |
|---|---|---|
| 50 kg | 1,750 ml | 2,250 ml |
| 60 kg | 2,100 ml | 2,600 ml |
| 70 kg | 2,450 ml | 3,100 ml |
| 80 kg | 2,800 ml | 3,500 ml |
| 90 kg | 3,150 ml | 3,900 ml |
| 100 kg | 3,500 ml | 4,350 ml |
Frequently Asked Questions
Is the 30-35 mL per kg rule medically accurate?
It is a clinical approximation used as a starting point, not a prescription. Actual needs vary with kidney function, climate, medication, diet water content, and physical activity. Older adults often need more per kg than younger adults. Use this estimate as a baseline and adjust based on thirst and urine colour.
How much water is in food?
About 20-30% of daily water intake comes from food. Fresh fruit and vegetables are 70-95% water by weight. A diet with substantial salad, fruit and cooked vegetables can contribute 600-800 mL per day. This is already partially accounted for in the 30-35 mL/kg guideline, which was developed assuming a typical mixed diet.
Does coffee or tea count toward daily water intake?
Yes. The mild diuretic effect of caffeine is smaller than the fluid intake from the drink itself, net hydration is positive. A 250 mL coffee contributes roughly 200-220 mL toward hydration. Alcohol is the main exception: it causes net fluid loss and should not be counted toward your daily target.