Water Intake Calculator
Estimate your daily water needs from body weight and activity level.
What is the Water Intake Calculator?
This tool estimates a reasonable daily water intake target from your body weight and activity level, using the widely cited 30–45mL-per-kilogram guideline rather than the oversimplified "8 glasses a day" rule, which isn't based on body size at all.
The formula
Daily Water (mL) = Body Weight (kg) × mL-per-kg factor, where the factor scales from 30mL/kg at rest up to 45mL/kg for intense exercise or hot climates.
How to use it
- Enter your body weight.
- Choose the activity level that best matches your typical day.
- Use the result as a daily target, counting all fluids, not just plain water.
This figure covers total fluid needs under normal conditions — it isn't adjusted for fever, pregnancy, breastfeeding, certain medical conditions, or very high caffeine/alcohol intake, all of which can shift real hydration needs. Anyone with a kidney, heart or liver condition that affects fluid balance should follow their doctor's guidance instead of a general formula like this one.
Want the "why" behind this tool? Read Why '8 Glasses a Day' Isn't Based on Your Body At All.