How Much Water Should I Drink? A Worked Example
A step-by-step worked example calculating daily water intake needs from body weight, exercise, and climate.
Rather than a flat "8 glasses" answer, here's how a weight-based hydration estimate actually gets calculated, step by step.
The formula
Baseline (ml) = weight (kg) × 35, + 350 ml per 30 min exercise, + 500 ml if hot/humid
Worked example
| Scenario | Calculation | Result |
|---|---|---|
| 160 lb (72.6 kg), 30 min exercise, temperate | 72.6 × 35 + 350 | 2,890 ml (≈2.89 L, 97.7 fl oz) |
| Same person, 60 min exercise, hot climate | 72.6 × 35 + 700 + 500 | 3,740 ml (≈3.74 L, 126.5 fl oz) |
Notice the second scenario needs roughly 30% more fluid than the first, purely from doubling exercise time and adding a hot climate — both meaningful adjustments a flat "8 glasses" rule would completely miss.
Enter your own weight, activity, and climate in the Water Intake Calculator for a personalized figure in liters, ounces, or glasses.