A baseline is not a prescription
A weight-based water estimate is useful for orientation, but it cannot see the temperature, humidity, altitude, clothing, illness, pregnancy, food moisture or how much you personally sweat. Two people completing the same workout may lose very different amounts of fluid.
Look for context
For ordinary daily life, thirst, meals and usual drinking patterns provide useful feedback for many healthy adults. Longer or hotter exercise needs more individual planning. Comparing body weight before and after a representative session can help estimate sweat loss, but it is still an imperfect snapshot.
More is not always safer
Drinking far beyond losses can also be harmful. Kidney, heart or endocrine conditions may require individualized fluid guidance. Treat the calculator as a broad starting range and seek professional advice when a medical condition, medication or persistent symptom affects fluid balance.