Water Intake Calculator
Body Weight Sets the Baseline, Activity Adds to It
Fluid needs scale with body size — a larger body has more tissue to hydrate and a larger surface area losing water through skin and breath — and then rise further with anything that increases sweat loss. This calculator builds a daily target from those two pieces separately, rather than defaulting everyone to a flat "eight glasses" figure that ignores both body size and how active the day was.
The Formula
Exercise Water (mL) = (Exercise Minutes ÷ 30) × 350
Total Daily Water = Base Water + Exercise Water
The 35 mL per kg figure is a commonly used baseline hydration estimate for adults; the exercise addition of roughly 350 mL per 30 minutes accounts for typical sweat loss during moderate activity.
Worked Example
| Component | Calculation | Amount |
|---|---|---|
| Base water | 70 × 35 | 2450 mL |
| Exercise water (30 min) | (30 ÷ 30) × 350 | 350 mL |
| Total | 2450 + 350 | 2800 mL (2.8 L) |
Climate, pregnancy, illness, and individual sweat rate all shift real-world needs above or below this baseline estimate.
Where This Number Is Actually Useful
- Endurance training — runners and cyclists use a baseline-plus-exercise target to plan fluid intake around long sessions.
- Hot-climate or physical-labor jobs — adding exercise minutes as a proxy for heat exposure gives a more realistic target than a flat daily number.
- General daily tracking — a concrete milliliter, ounce, or cup target is easier to hit consistently than a vague "drink more water" reminder.
How to Use This Calculator
- Choose Metric (kg) or Imperial (lb) units.
- Enter your body weight.
- Enter your exercise minutes for the day (leave at zero on rest days).
- Select Calculate to see your total daily water target in liters, ounces, and cups.
Related Calculations
Pair this with the Body Water Calculator to see how much of your current weight is already water, or the TDEE Calculator to plan the calorie side of an active day.