Calculator
Hydration Calculator
Explore a general daily fluid target based on your body weight and activity level.
Hydration Calculator
Enter your weight to estimate a daily fluid target.
This tool is for education and general interest only. It is not a medical device and must not be used to diagnose, treat or make health decisions. Always consult a qualified professional.
How to use it
- Step 1Enter your body weight.
- Step 2Choose your activity level.
- Step 3See a general daily fluid estimate.
Why hydration matters
Water makes up roughly 60% of the adult body and is involved in nearly every process, from carrying nutrients to controlling temperature.
There is no single correct amount for everyone. Needs depend on body size, activity, climate, diet and health.
About this estimate
This tool uses a common teaching rule of about 35 millilitres of fluid per kilogram of body weight, with a small allowance for activity. Remember that food, especially fruit and vegetables, also supplies water.
Learn more in our guide to water in the human body and kidney function, or read the article on hydration facts.
Questions & Answers
Frequently asked questions
The "8 glasses" rule is a rough guide, not a strict requirement. Your needs depend on size, activity and climate, and drinks and food both count.
Very rarely, drinking far too much in a short time can be harmful. For most people, thirst is a reliable guide.
Yes. Most fluids, including tea and coffee, contribute to your daily total.
Understand the science
Go beyond the numbers
Every tool pairs with a guide that explains the biology behind it in plain language.