Water Intake by Activity Calculator

How it is calculated

The tool adds a weight-based baseline to an exercise allowance: baseline = weight × 35 mL, exercise = minutes × 12 mL, and total = baseline + exercise, shown in litres (÷ 1000). Weight is in kilograms and exercise is the number of minutes you are active that day. Both constants are fixed in the tool, so every minute counts the same whether it is a walk or a hard run, and heat, humidity, age, health conditions and body size beyond weight are not considered. Zero minutes is allowed and returns the baseline alone. The tool shows no result for a weight below 2 kg or above 650 kg, for negative minutes, or for more than 1,440 minutes (a full day). Treat the result as a starting estimate, not a medical target.

Common mistakes

• Entering weight in pounds. The field is in kilograms, so 154 typed in place of 70 kg gives a baseline of 5.39 L.
• Entering the total hours as minutes, or the other way round. 45 minutes of exercise is 45, not 0.75.
• Counting the whole day as exercise. Only time actually active counts, and 1,440 minutes still produces an unrealistic 19.73 L for a 70 kg person; anything above 1,440 gives no result.
• Assuming the total is all plain water. Food and other drinks supply part of daily fluid intake, so the figure is not meant to be drunk entirely as water.
• Using the same result for hot-weather or long endurance sessions. The allowance is a flat 12 mL per minute and does not rise with heat or sweat rate.