💧 Water Intake Calculator
Estimate daily water intake from body weight and activity level.
About this tool
Estimates a daily water intake target using a common baseline of about 33 mL per kilogram of body weight, with an added percentage for moderate or high activity levels or hot climates that increase fluid loss through sweat.
This is a general starting-point estimate — actual hydration needs vary with climate, individual physiology, diet, and health conditions, and total fluid needs also include water from food and other beverages, not just plain water.
Worked example
A 70 kg person with moderate activity gets an estimated target of about 3.1 liters (roughly 105 fl oz) per day.
How to use it
- Choose kilograms or pounds.
- Enter your body weight.
- Select an activity level reflecting your typical day.
- Press Estimate daily water intake.
Tips
- This estimate is for total fluid intake context, not just plain drinking water — food and other beverages also contribute to daily hydration.
- Hot or humid climates, illness, and intense exercise all increase fluid needs beyond a baseline estimate.
- Thirst and urine color are practical everyday indicators of hydration status alongside any calculated target.
FAQ
Is "8 glasses a day" the same as this estimate?
The classic 8-glasses guideline (about 1.9 liters) is a simplified rule of thumb; this calculator scales the target to body weight and activity, which usually gives a different, more individualized number.
Does this include water from food?
No — this estimates a fluid intake target broadly; a meaningful portion of daily hydration in a typical diet does come from food, particularly fruits and vegetables, which this simple calculator doesn't separately account for.
Should I drink more in hot weather?
Yes — select a higher activity level to account for increased fluid loss from heat or intense exercise, though individual needs still vary and this remains a general estimate.
From the blog: getting the most out of this tool
Hydration advice online ranges from oddly specific daily gallon targets to vague "drink more water" reminders, so we aimed for something in between — a number that at least scales sensibly with body size and activity rather than being a single one-size-fits-all figure.
As with several of our health tools, this is meant as a reasonable starting estimate to build a habit around, not a precise physiological requirement calculated specifically for your body.