Daily Water Intake Formula
30–35 ml/kg covers most adults at rest. Add 350–500 ml per hour of exercise, plus sweat losses on hot days. Urine straw-yellow color is a better real-world signal than any single number.
Formula
Copy the exact expression or work through it step by step below.
water_ml = mass_kg × ml_per_kg + exercise_hours × ml_per_hour
baseline 30–35 ml/kg sedentary, 35–40 ml/kg active. Exercise: +400 ml/hour typical. Variables
mass_kg
Body mass
Kilograms.
ml_per_kg
Baseline rate
30 ml/kg sedentary, 35 ml/kg active, 40 ml/kg hot climate or pregnancy/lactation.
exercise_hours
Daily exercise hours
Sum of moderate-to-vigorous training duration.
ml_per_hour
Exercise add-on
300–400 ml/hour cool conditions, 500–800 ml/hour hot conditions or intense work.
Step By Step
- 1
Pick the baseline rate that matches your activity level and climate.
Office worker who trains 4×/week → 35 ml/kg.
- 2
Multiply by body mass.
78 kg × 35 ml/kg = 2,730 ml baseline.
- 3
Add exercise replacement: estimate hours × ml per hour.
1 hour gym session + 30 min walk = 1.5 hours × 400 ml = 600 ml extra.
- 4
Sum and round. Roughly 20% of fluid comes from food (fruit, soup, vegetables), so total beverages can be ~80% of the number.
2,730 + 600 = 3,330 ml total fluid. Beverages target ≈ 2,664 ml.
Worked Example
78 kg active adult, 1.5 h training/day
Body mass (kg)
78
Baseline (ml/kg)
35
Training hours
1.5
water = 78 × 35 + 1.5 × 400 = 2,730 + 600 = 3,330 ml/day
Total fluid 3.3 L/day, of which ~2.7 L from beverages. Hot weather sessions can push the total above 4 L.
Common Variations
Try These Tools
Run the numbers next
Sweat Rate Calculator
Calculate your personal sweat rate from pre/post-exercise weigh-ins and estimate fluid and sodium losses using ACSM guidelines.
Calories Burned Calculator
Estimate exercise calorie burn from body weight, duration, MET intensity, and incline.
Sources & References
- EFSA Panel on Dietetic Products. Scientific Opinion on Dietary Reference Values for water — European Food Safety Authority (2010)
- ACSM Position Stand: Exercise and Fluid Replacement — Medicine & Science in Sports & Exercise