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Hydration Calculator
How much water your body actually needs — adjusted for your weight, activity, and climate. With the electrolyte context most calculators skip.
Your details
This estimates total daily water intake from all sources including food (~20%). Your actual need varies day to day.
Daily Target Glasses
Daily target: 12 glasses.What this means
Your estimated daily need of 3.1 litres reflects higher demands from your activity level and environment. At this volume, hydration directly affects exercise performance, recovery speed, and cognitive clarity. Your body is losing meaningful amounts of water through sweat, respiration, and metabolic processes — replacing it consistently matters more than the total number.
What to consider
At this volume, plain water alone is not enough — electrolyte balance is essential. Consider a daily electrolyte supplement or deliberate dietary sources of sodium, potassium, and magnesium. Dehydration at this activity level can meaningfully affect blood glucose readings and insulin sensitivity — your Blood Glucose Interpreter and HOMA-IR results are most reliable when hydration is consistent.
Medications that may affect your result
Diuretics (hydrochlorothiazide, furosemide, chlorthalidone) significantly increase fluid loss through urination. If you are on a diuretic, your water needs may be substantially higher than this estimate. Monitor for signs of dehydration including dizziness, dark urine, and fatigue.
Lithium requires careful hydration management. Dehydration can increase lithium levels to toxic concentrations. If you are on lithium, maintaining consistent fluid intake is critical — discuss your specific target with your prescribing provider.
SGLT2 inhibitors (empagliflozin, dapagliflozin) increase glucose excretion through urine, which increases fluid loss. Additional hydration is recommended while on these medications.
If you are taking any of these medications, discuss your hydration targets with your healthcare provider. This calculator provides a general estimate that may not account for medication-specific fluid needs.
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About this tool
Formula
Base intake: body weight (kg) × 0.033 litres. Activity multipliers: sedentary ×1.0, lightly active ×1.15, moderately active ×1.25, very active ×1.5. Climate multipliers: temperate ×1.0, warm ×1.1, hot/humid ×1.2. Based on IOM and EFSA hydration guidelines.
Electrolyte Context
Most hydration calculators focus only on volume. This tool includes electrolyte context because water balance depends on sodium, potassium, and magnesium. At intake levels above 3 litres, drinking plain water without electrolytes can contribute to dilutional hyponatremia, especially during prolonged exercise or heat exposure.
Known Limitations
This is a population-level estimate. Individual hydration needs vary based on body composition, metabolic rate, dietary water content (~20% of intake comes from food), caffeine consumption, altitude, humidity, and individual sweat rate. Pregnant and breastfeeding women, people with kidney conditions, and those on diuretics or lithium should consult their provider for specific targets. This calculator does not account for acute illness, fever, or vomiting/diarrhea, all of which significantly increase fluid needs.
Sources
Institute of Medicine. Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate. National Academies Press, 2005. EFSA Panel on Dietetic Products. Scientific Opinion on Dietary Reference Values for Water. EFSA Journal, 2010.
Educational tool only. Not for diagnostic purposes. Consult a healthcare provider for medical decisions.