{
  "slug": "water-intake",
  "title": "Water Intake Calculator",
  "category": "Macros & Intake",
  "category_slug": "macros-intake",
  "tier": 2,
  "summary": "Estimate daily water intake using body weight and activity level with clinical hydration guidelines.",
  "description": "This calculator estimates daily water intake in millilitres by applying a clinical hydration guideline of 35 ml per kilogram of body weight plus 12 ml per minute of physical activity. It requires weight in kilograms and activity duration in minutes, then outputs a baseline hydration target and an activity-adjusted total. The formula reflects European Food Safety Authority (EFSA) adequate-intake recommendations and American College of Sports Medicine (ACSM) exercise-hydration guidance for healthy adults.",
  "page_url": "https://fitmetriclab.com/en/tools/macros-intake/water-intake/",
  "api_url": "https://fitmetriclab.com/api/tools/water-intake.json",
  "formula": {
    "id": "water_intake",
    "expression": "V_{ml} = 35\\,w_{kg} + 12\\,t_{min}",
    "variables": [
      {
        "symbol": "w",
        "description": "Weight in kg"
      },
      {
        "symbol": "a_{adj}",
        "description": "Activity adjustment in ml"
      }
    ]
  },
  "inputs": [
    {
      "id": "weight_kg",
      "label": "Weight",
      "type": "number",
      "unit": "kg",
      "default": 75,
      "min": 20,
      "max": 300,
      "step": 0.1
    },
    {
      "id": "activity_minutes",
      "label": "Activity",
      "type": "number",
      "unit": "min",
      "default": 60,
      "min": 0,
      "max": 600,
      "step": 5
    }
  ],
  "worked_example": {
    "inputs": {
      "weight_kg": 75,
      "activity_minutes": 60
    },
    "expected_output": "3,345 ml"
  },
  "result_summary_template": "For a body weight of {weight_kg} kg and {activity_minutes} minutes of daily activity, the calculator estimates adequate daily water intake at {result}.",
  "methodology": "Daily water (ml) = 35 × weight_kg + 12 × activity_minutes. The 35 ml/kg base is the widely cited clinical rule of thumb, consistent with EFSA adequate-intake guidance. The 12 ml/min activity adjustment corresponds to ~350–400 ml per 30-minute session, within ACSM exercise-hydration recommendations.",
  "sources": [
    {
      "label": "European Food Safety Authority. Dietary Reference Values for Water. EFSA Journal. 2010.",
      "url": "https://www.efsa.europa.eu/en/efsajournal/pub/1459"
    },
    {
      "label": "Sawka MN, Burke LM, et al. American College of Sports Medicine Position Stand: Exercise and Fluid Replacement. Med Sci Sports Exerc. 2007.",
      "url": "https://pubmed.ncbi.nlm.nih.gov/17277604/"
    },
    {
      "label": "Institute of Medicine. Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate. National Academies Press. 2005.",
      "url": "https://www.nap.edu/catalog/10925/dietary-reference-intakes-for-water-potassium-sodium-chloride-and-sulfate"
    }
  ],
  "faqs": [
    {
      "question": "Why does the calculator use 35 ml per kilogram?",
      "answer": "The 35 ml/kg baseline reflects adequate intake figures published by the European Food Safety Authority and appears in clinical hydration references across North America and Europe. It represents a middle-ground estimate for adults in temperate climates with moderate activity levels."
    },
    {
      "question": "How does the activity adjustment work?",
      "answer": "The calculator adds 12 ml for every minute of physical activity entered. This corresponds to approximately 350–400 ml per 30-minute moderate-intensity session, within the American College of Sports Medicine's recommended range of 500–600 ml per 30–60 minutes of exercise. The tool applies a slightly more conservative multiplier to avoid overestimation."
    },
    {
      "question": "Does the calculator account for food-derived water?",
      "answer": "No. The output reflects fluid intake from beverages. Typical diets contribute 20–30% of total water intake through soups, fruits, vegetables, and other water-rich foods. The calculator provides a reference for drinking water and other beverages, not total water turnover."
    },
    {
      "question": "What factors can increase fluid needs beyond the calculated amount?",
      "answer": "High ambient temperatures, low humidity, altitude above 2,500 meters, prolonged outdoor endurance training, high individual sweat rate, illness with fever or gastrointestinal fluid loss, pregnancy, and lactation can all increase requirements. The formula assumes temperate indoor conditions and moderate exercise intensity."
    },
    {
      "question": "Can I use this calculator if I have a medical condition?",
      "answer": "This tool is educational only and does not replace medical guidance. Kidney disease, heart failure, hyponatremia, electrolyte disorders, and certain medications (diuretics, lithium, NSAIDs) require individualized fluid-intake plans. Consult a physician or registered dietitian before using any hydration estimate if you have a diagnosed condition."
    }
  ],
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    {
      "slug": "protein-intake",
      "title": "Protein Intake Calculator",
      "api_url": "https://fitmetriclab.com/api/tools/protein-intake.json",
      "page_url": "https://fitmetriclab.com/en/tools/macros-intake/protein-intake/"
    },
    {
      "slug": "macro-split",
      "title": "Macro Split Calculator",
      "api_url": "https://fitmetriclab.com/api/tools/macro-split.json",
      "page_url": "https://fitmetriclab.com/en/tools/macros-intake/macro-split/"
    },
    {
      "slug": "alcohol-calories",
      "title": "Alcohol Calories Calculator",
      "api_url": "https://fitmetriclab.com/api/tools/alcohol-calories.json",
      "page_url": "https://fitmetriclab.com/en/tools/macros-intake/alcohol-calories/"
    }
  ],
  "last_updated": "2026-04-22",
  "price": {
    "value": 0,
    "currency": "USD"
  },
  "runs_in_browser": true,
  "disclaimer": "Educational estimate produced from a published formula. Not medical, nutritional, or training advice. Calculations are deterministic — apply the formula to the inputs to reproduce the result."
}