Water Intake During Exercise Calculator

How it is calculated

The tool starts with a base hourly rate for the intensity you pick: 400 ml/h for light, 600 ml/h for moderate (the default) and 800 ml/h for vigorous exercise. An empty intensity is treated as moderate, but an intensity other than light, moderate or vigorous gives no result. That rate is scaled to your size against a 70 kg reference: rate = base × weight ÷ 70. Then total ml = rate × minutes ÷ 60 and ounces = ml ÷ 29.5735 (US fluid ounces). Weight in kilograms (2 to 650) and duration in minutes (above zero) are required; outside those limits there is no result. The rates are fixed estimates; they do not know your sweat rate, the temperature or humidity, or what the drink contains, and the result is a planning figure for the whole session, not a reason to drink on a schedule regardless of thirst.

Common mistakes

• Entering the workout duration in hours. The field is minutes, so a 1.5-hour session must be typed as 90, otherwise the total is 60 times too small.
• Mixing up the two units in the output. The millilitre total and the ounce total are the same amount; the ounce value is US fluid ounces, not UK ones.
• Treating the total as the amount to drink all at once. It is spread over the session, and the per-hour rate is the number to pace yourself against.
• Typing an intensity name the tool does not know. Anything other than light, moderate or vigorous gives no result at all; only a blank intensity falls back to moderate, so leaving it empty by accident gives the lower moderate figure.
• Using the total on a very long event as if it replaced sodium. Water only; the tool does not add electrolytes, which matter in long, hot sessions.