About this tool
Use the number to plan your day
How Much Water Today answers one practical question: roughly how much fluid should you plan for today, given your body size, sweaty activity, and conditions?
What to do with the result
Treat the center number as a convenient planning target and the range as the more honest answer. Spread drinks across the day. Thirst, sweat, urine color, meals, and how you feel can help you adjust.
Why it changes day to day
A quiet day indoors is not the same as an hour-long workout outside in humid weather. The two quick condition inputs make “today” part of the calculation instead of returning the same static number every day.
What it cannot tell you
A browser calculator cannot measure your sweat rate, diagnose dehydration, account for every medication, or know whether a clinician has told you to restrict fluids. It is not medical advice and should not override individual care.
Your inputs stay on your device
The calculation runs in your browser. The calculator does not require an account and does not send your weight or answers to a calculation service.