Last updated 23 August 2026
How the target is worked out
The baseline is roughly 33ml per kilogram of body weight — a commonly cited middle-ground figure from hydration research for a sedentary adult in a temperate climate. Activity adds to that: more exercise means more fluid lost to sweat, so the target rises with how active you say you are.
What this doesn't account for
Hot weather, altitude, illness, and pregnancy or breastfeeding all increase real fluid needs beyond what this calculator shows. It also only counts water specifically — food and other drinks contribute a meaningful share of daily fluid too, so this is a sensible target rather than the total amount you need to drink.
Common questions
Where does the 33ml per kg figure come from?
It's a commonly cited middle-ground estimate from hydration research, roughly 30–35ml per kilogram of body weight per day for a sedentary adult in a temperate climate. Individual needs vary with climate, health conditions and sweat rate.
Does this count water from food and other drinks?
No, this is a target for water specifically. In practice a meaningful share of daily fluid comes from food and other beverages, so this figure is a reasonable target rather than the only fluid you need to drink.
Is more water always better?
No. Drinking far beyond what your body needs can dilute sodium levels and cause genuine harm in extreme cases. This is a general target, not a floor to push past — thirst and urine colour are reasonable everyday guides too.