How the hydration estimate works
Water needs vary with body size, activity, temperature, humidity, food, health, and altitude. This calculator starts with 0.033 litres per kilogram, adds 0.35 litres for each 30 minutes of exercise, and adds 0.5 litres for hot or humid conditions. It shows litres, millilitres, and approximate 500 millilitre bottles.
This is a practical planning goal, not a medical prescription. Water also comes from food and other drinks, and your needs may be lower or higher. During long or intense exercise, electrolytes and a personalised fluid plan may matter. Spread fluids through the day instead of forcing a large amount at once.
People with heart, kidney, or liver conditions may need fluid limits and should follow their clinician’s advice rather than a general calculator. Infants and young children have different needs.
Frequently asked questions
Should I drink exactly this amount?
No. Treat it as a starting point and adjust for thirst, losses, medical guidance, and conditions.
Why are hot climates included?
Heat and humidity can increase sweat losses, so the estimate adds a modest planning adjustment.