Water Intake Calculator for Hot Weather & Outdoor Work

How much water should you drink in hot weather or outdoor work? A daily target adjusted for heat, humidity, and heavy sweating — sweat-rate guidance included.

Heat changes the arithmetic of hydration. Once temperatures climb past roughly 25°C — or humidity blocks sweat from evaporating — fluid losses can reach a litre per hour even at rest, and two or more during physical work. Construction crews, farm workers, and anyone caught in a heat wave face the same equation: the daily baseline below, plus whatever the day evaporates out of you. This calculator sets that baseline from your weight, age, and sex at an outdoor-work activity level; run the climate check under the form to add your local heat-and-humidity multiplier, then sip steadily through the day rather than saving it all for the evening.

Key points for this goal
  • Baseline from your body weight, preset to an outdoor-work activity level
  • Run the climate check to add your local heat and humidity multiplier
  • Heavy sweating can pass 1 litre per hour — spread replacement across the shift
  • Include electrolytes or salty food on long, hot shifts, not just plain water
Calculate your target

Prefilled for this goal — adjust anything to match you.

Personal Details
Age Group
Activity Level

intense - 60–90 minutes of intense physical activity.

RestingLightModerateIntenseExtreme
Health & Lifestyle Factors
Climate

Adjust for your local weather. We look up temperature, humidity, and elevation for your area — your health details never leave this page.

Water Intake Calculator for Hot Weather & Outdoor Work — FAQ

How much extra water should I drink in a heat wave?

Plan on roughly 0.5 to 1 litre extra per hour of heavy sweating beyond your baseline — more for larger bodies doing physical work in full sun. The climate check under the calculator adds a percentage for your local conditions, which covers day-to-day variation. Drink steadily every 15-20 minutes while working; a litre all at once mostly ends up as urine.

Does drinking very cold water help in the heat?

Cool fluids are absorbed just as well and are more palatable, which genuinely helps people drink enough in the heat — around 15-21°C is the practical sweet spot. What matters more is total volume and sodium: on long sweaty shifts, plain water alone can dilute blood sodium, so alternate with electrolyte drinks or salty snacks.