Estimates a starting point for daily water intake based on body weight, using a widely cited general guideline.
How it works
Body weight in kilograms is multiplied by approximately 33 milliliters per kilogram to give a suggested daily intake in liters.
What this does not include
This is a general starting estimate, not a clinical requirement — actual needs vary significantly with climate, activity level, and individual health, and this does not account for any of those factors.
How to use this calculator
- Enter your body weight.
A worked example
Body weight 70 kg × 0.033 L/kg = 2.31 L per day. Body weight 90 kg × 0.033 L/kg = 2.97 L per day.
What the variable means
| Variable | Meaning |
|---|---|
| Body weight | The only input — multiplied by a fixed 0.033 L/kg rule of thumb |
Edge cases worth knowing
This is a starting point, not a ceiling or a requirement. Climate, activity level, and individual health all shift real hydration needs above or below this baseline, none of which this simple weight-based estimate accounts for.
Heavier body weight doesn’t necessarily mean proportionally more water is needed in every case — the linear rule is a simplification; body composition and other factors matter too.
Frequently asked questions
Is this the same as the “8 glasses a day” rule?
Not exactly — the 8-glasses guideline is a flat number regardless of body size, while this estimate scales with your actual weight, giving a more individualized starting point.
Does exercise increase how much water I need?
Yes — this calculator doesn’t account for activity level, so treat the result as a baseline and add more on days with significant exercise or heat exposure.
What’s a better day-to-day guide than a fixed number?
Thirst and urine color are generally considered more responsive, individualized indicators of hydration status than any single calculated target.
This calculator is for general informational purposes only and does not constitute medical advice. Consult a qualified healthcare professional for guidance specific to your situation.
