Hydration Calculator
Estimate your daily water requirement based on weight, weather and activity.
Last updated 10/08/2026
Calculator
Hydration Calculator inputs
Enter your weight.
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Manage My Service DetailsHow this works
What it means
A general daily water intake target based on your body weight, adjusted for hot weather and higher activity levels.
How it’s calculated
Uses a commonly-cited baseline of about 35 mL of water per kg of body weight per day, plus additional water for hot weather and for higher activity levels.
Common Defence use cases
A quick daily hydration target, especially useful ahead of field duty, hot-weather postings, or increased physical training.
Formula
Baseline = Weight (kg) × 35 mL
Daily Water Requirement = Baseline + Weather Adjustment + Activity AdjustmentAssumptions
- General practical guidance only, not medical advice — actual fluid needs vary by individual, climate, altitude and health conditions. Consult a medical professional if you have a condition affecting fluid intake.
- The 35 mL/kg baseline and the weather/activity adjustments are commonly-cited general hydration guidelines, not a medical or Defence-specific standard.
- Does not account for fluid from food, or for medical conditions requiring fluid restriction — consult a medical professional in those cases.
Example calculations
Weight 70 kg, Normal weather, Moderate activity
Daily Water Requirement 3.0 L (baseline 2.45 L + 0.5 L extra)
Weight 80 kg, Very Hot weather, High activity
Daily Water Requirement 4.8 L (baseline 2.8 L + 2.0 L)