Daily fluid needs vary substantially between people and circumstances. This calculator provides an adjustable estimate from body weight, a user-selected base water rate, exercise time, and an optional activity-water allowance.
How it works
Enter your weight and exercise minutes, then review the two editable assumptions: the base water rate in mL per kg per day and the extra water assigned to each 30 minutes of activity. The defaults are calculation examples, not universal medical recommendations.
The formula
The result estimates fluid from the assumptions you enter. Actual needs vary with climate, sweat rate, diet, pregnancy, illness, medications, and other factors. Total water intake also includes water from food and other beverages.
Worked example
Example only: at 70 kg, a base rate of 35 mL/kg/day, 30 minutes of activity, and an activity allowance of 350 mL, the calculator returns 2.8 L/day. Change either assumption when a different basis is appropriate.
This calculator is an adjustable planning estimate, not an individualized hydration prescription. Its default rates are examples and can be changed.
Frequently asked questions
Is 35 mL/kg a universal daily requirement?
No. It is used here only as an editable starting assumption. Authoritative dietary-reference guidance expresses water intake using age, sex and life-stage reference values rather than one universal body-weight formula.
Does the result mean I must drink that amount as plain water?
No. Total water intake can come from drinking water, other beverages, and water contained in food. The calculator should be treated as an estimate rather than a prescription for plain-water intake.
Should I automatically add 350 mL for every 30 minutes of exercise?
No. That value is an editable estimating assumption. Exercise fluid losses vary greatly with intensity, duration, temperature, humidity, clothing, body size and individual sweat rate.
When should I use medical advice instead of this estimate?
Individual fluid targets can require professional guidance, especially with kidney or heart disease, pregnancy, significant illness, medications affecting fluid balance, or prolonged strenuous exercise.