THE NUMORIX GUIDE
How to use the Hydration Calculator
Last reviewed September 14, 2026
What this calculator does
The calculator starts with base = weight * 0.
Formula and method
The calculator starts with base = weight * 0.033 liters. It adds 0, 0.3, 0.5, 0.8, or 1.0 liters for activity levels 1-5, adds 0.3 for hot or 0.5 for humid climate, and adds 0.5 + (exerciseMinutes / 30) * 0.5 whenever exercise minutes are above zero. Cups are liters * 4.22675.
Variables and inputs
Weight is in kilograms, activity level is a numeric 1-5 field, climate is normal, hot, or humid, and exercise is minutes. The UI does not enforce the 1-5 range at calculation time. Results are rounded to two decimals in liters and one decimal in cups.
Worked example
For 70 kg, activity level 2, normal climate, and 30 exercise minutes: base = 70 * 0.033 = 2.31 L; activity adds 0.30 L; exercise adds 0.5 + (30 / 30) * 0.5 = 1.00 L; total = 3.61 L, or 3.61 * 4.22675 = 15.3 cups after display rounding.
How to interpret the result
This is a route-specific planning estimate, not a measured hydration requirement. It combines body weight with fixed adjustments; the output should be compared with thirst, sweat losses, environment, food and beverage water, and any medical fluid plan.
Common mistakes to avoid
Enter kilograms, not pounds, and use the activity field as the intended 1-5 level rather than exercise minutes. Remember that any positive exercise time adds a 0.5-liter baseline before the time-based increment, and cups here are US cups.
Assumptions and limitations
The formula does not account for age, sex, pregnancy, breastfeeding, altitude, sweat rate, illness, food moisture, electrolytes, kidney disease, heart failure, or fluid restrictions. It can recommend an unsuitable amount because its adjustments are fixed and the UI does not validate activity or negative exercise input.