A weight-based rule with fixed activity and climate additions. It is not the EFSA method or a clinically validated personal recommendation.
Before using the result
For adult educational use only. Do not use this estimate to manage illness, pregnancy, breastfeeding, children’s needs or endurance-event hydration. If you have a fluid restriction or a clinician’s plan, follow that plan rather than this number.
How this estimate is calculated
Weight in kg × 0.033, plus 0 / 0.5 / 1 / 1.5 L for the four activity settings and 0.5 L for hot/humid conditions. These are this tool’s fixed assumptions, not prescribed fluid amounts.
This number is not an amount of plain water to drink. The tool does not separate water from food and drinks.
What this water calculator actually estimates
This calculator multiplies weight in kilograms by 0.033 and adds fixed amounts for activity and climate. It does not implement EFSA Adequate Intake values or an ACSM exercise-hydration protocol. There is no clinical validation supplied for this combination of assumptions. The formula does not account for age, pregnancy, breastfeeding, medication, illness, exercise duration or measured sweat loss. Choosing a higher activity level adds a fixed amount; it does not measure how much fluid you lose.
Water references are not personal prescriptions
EFSA’s adult reference values concern total water from food and beverages under moderate conditions. They are different from a target for plain water alone, and they are not the formula used here. The NHS also distinguishes general fluid guidance from individual needs. Do not force yourself to drink to match the displayed volume or glass count. This tool cannot assess dehydration or determine a safe fluid allowance. Medical fluid restrictions and individual care plans take priority.
- Weight can be entered in kilograms or pounds
- Fixed activity and climate assumptions are shown above the inputs
- Calculated volume is rounded to one decimal place
- 250 mL equivalents are a unit conversion, not a drinking goal
- The calculation runs locally in your browser
Free. No signup. Your inputs stay in your browser. Ads via Google AdSense (consent required).
Frequently asked questions
Is this the EFSA formula?
No. This tool uses weight × 0.033 plus fixed additions for activity and climate. It does not calculate EFSA Adequate Intake values, and those references do not validate this combination.
Should I drink the displayed number of glasses?
No. The glass count is only a conversion of the calculated volume into 250 mL equivalents, rounded up. The tool does not separate water in food from drinks and does not set a personal drinking target.
Can this plan my hydration during exercise?
No. It does not measure sweat loss or ask how long you exercise. The activity additions are fixed assumptions, not an individualized fluid-replacement plan.
What if I have a prescribed fluid allowance?
Follow the allowance or care plan given by your healthcare team. Do not increase your intake to match this calculator.
Can I use this for children or during pregnancy?
This estimator is not designed for children, pregnancy, breastfeeding or medical conditions. Seek guidance appropriate to that situation rather than adapting this number.
References and scope
These sources explain the context and limitations; they do not validate this tool’s weight-based formula.
By Marco B. ·