Water Intake Calculator
Advanced hydration utility using Lean Body Mass, METs, and vapor pressure analysis. Calculates fluid, electrolyte needs, and intake schedules.
About
Standard hydration advice often leads to error because it ignores body composition and specific environmental thermodynamics. Muscle tissue contains approximately 75% water, whereas adipose tissue contains only 10%. A calculator relying solely on total body mass will overestimate needs for individuals with high body fat and underestimate needs for lean athletes.
This tool utilizes the Boer Formula to determine Lean Body Mass (LBM) as the primary scalar. It integrates the Beverage Hydration Index (BHI), differentiating between pure water, electrolyte solutions, and diuretics. It further accounts for Respiratory Water Loss (RWL) at altitude and Cutaneous Evaporation derived from specific Metabolic Equivalent (MET) intensity tables. It provides a safeguard against both dehydration and exercise-associated hyponatremia.
Formulas
The algorithm first isolates Lean Body Mass (LBM) to establish the Basal Hydration Requirement (Hbase). The Boer formula estimates LBM:
Total fluid need Vtotal aggregates basal needs, active sweat loss (Sloss), and respiratory loss (Rloss):
Where Cenv is the environmental coefficient derived from temperature and humidity. Sodium requirements are calculated via:
Reference Data
| Activity / Condition | MET Intensity | Avg Sweat Rate (L/hr) | Sodium Loss (mg/L) |
|---|---|---|---|
| Resting / Desk Work | 1.3 | 0.1 | 200 |
| Walking (Moderate) | 3.5 | 0.4 | 400 |
| Weight Training (Heavy) | 6.0 | 0.7 | 600 |
| Running (10 km/h) | 9.8 | 1.2 | 900 |
| Cycling (Vigorous) | 8.5 | 1.1 | 850 |
| Hot Yoga (Bikram) | 3.0 | 1.5 | 1100 |
| Swimming (Laps) | 8.0 | 0.9 | 500 |
| Hiking (Altitude >2000m) | 6.5 | 0.8 + RWL | 700 |
| Construction / Manual Labor | 5.5 | 0.8 | 1000 |
| Combat Sports (Sparring) | 11.0 | 1.8 | 1200 |