Formula, in Nutrition Planning

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.

4 variables. Published Mar 12, 2026. Updated May 10, 2026. By AI Fit Hub.

Education, not medical advice. The result comes only from the published formula and your inputs. How we check our formulas.

Formula

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)

Baseline (ml/kg)

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

Sweat-rate-based protocol (pre-/post-weigh-in): replace 125–150% of body-weight lost per hour during exercise.

EFSA adequate intake: 2.0 L/day (women), 2.5 L/day (men) for sedentary adults in temperate climates — total fluid including food.

Caffeine and moderate alcohol have a net hydrating effect when consumed habitually; the 'caffeine dehydrates' framing was overstated.

Run the numbers next

Recovery Sweat Rate Calculator
Calculate your personal sweat rate from pre/post-exercise weigh-ins and estimate fluid and sodium losses using ACSM guidelines.
Cardio Calories Burned Calculator
Estimate exercise calorie burn from body weight, duration, MET intensity, and incline.

Sources

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