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.