Water Intake Formula Explained
Compare official water reference values with the site’s clearly labeled 30–40 mL/kg/day heuristic.
The formula used by this site’s weight tool
The calculator applies a rule of thumb: weight in kilograms × 30 to 40 mL per kilogram per day. For 70 kg, that gives 2,100–2,800 mL, or 2.1–2.8 L. This is the site’s chosen heuristic, not a clinical requirement or official recommendation.
What an official reference means
The National Academies gives adult Adequate Intakes for total water, including food and beverages: 3.7 L/day for men and 2.7 L/day for women ages 19–50. An AI is a population-level reference, not an individual’s minimum or prescription. Read the National Academies summary.
The approaches answer different questions
A weight multiplier scales output to body mass but does not model diet, activity, climate, illness, pregnancy, medicines, or kidney and heart function. A population AI summarizes a reference group. Neither should be mistaken for an individualized medical assessment.
Check units before comparing
Convert pounds to kilograms before applying mL/kg. Divide milliliters by 1,000 for liters, or multiply liters by about 33.814 for US fluid ounces. The calculator handles conversions and rounds the displayed result; rounding does not make an estimate more precise.
Common questions
Is 30–40 mL/kg/day official medical guidance?
No. The site labels it as a rough heuristic, not a clinically validated formula.
Does this calculate plain water?
It does not separate plain water from other drinks or food moisture.
Why may the result differ from an adult AI?
The weight heuristic and population-level AI use different methods and assumptions.
Sources and further reading
Sources support the specific guidance described above. This page is general information, not diagnosis or individualized medical advice.