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● Metabolism & diet

Know exactly how much water to drink every day.

Calculate your ideal daily water intake from body weight, activity level and climate. Results in mL, glasses and fl oz — with a visual hydration indicator.

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Water Intake — Daily Hydration
mL · glasses · fl oz based on weight, activity and climate
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Your data

lb
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Your result

— mL
—
Enter your data above
Daily water rounded to nearest 50 mL—
In glasses 250 mL each—
In fl oz US fluid ounces—
Base (weight only)—
Activity bonus—
Climate bonus—
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How it's calculated

Weight-based hydration with activity and climate adjustments

This water intake calculator uses 35 mL per kilogram of body weight as the baseline — a widely cited reference range — then adds fluid for activity level and climate. For a 70 kg (154 lb) moderately active person in a temperate climate the result is 3,450 mL (about 13.8 glasses or 116.6 fl oz). Results are rounded to the nearest 50 mL for practical use.

The 35 mL/kg/day base comes from general nutrition guidelines. Activity increases insensible losses through sweat, while hot or humid climates can raise sweat rate to 1–2 L/hour during exercise. The calculator adds fixed bonuses for each tier rather than a continuous formula, making results easy to verify and apply.

Base = 35 mL × weight (kg)
Total = Base + Activity bonus + Climate bonus
Activity: +0 / +500 / +1000 / +1500 mL
Climate: +0 / +300 mL
  1. 1
    Convert weight to kg (if imperial) and compute base
    —
  2. 2
    Add activity-level bonus
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  3. 3
    Add climate bonus
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  4. 4
    Round to nearest 50 mL and convert to glasses and fl oz
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Understand the terms

Hyponatremia
Dangerously low blood sodium caused by over-hydration, most common in endurance athletes who drink excessive plain water. Balance large intakes with electrolytes.
Electrolytes
Minerals (sodium, potassium, magnesium, chloride) dissolved in body fluids. They regulate fluid balance, nerve signals and muscle contractions. Important when sweating heavily.
Dehydration signs
Dark yellow or amber urine, dry mouth, fatigue, headache, and reduced concentration are early warning signals. Losing just 1–2% of body weight in fluid can impair performance.
See the full glossary →
Disclaimer: estimation tool for informational and planning purposes, based on general nutrition reference values (2026). Actual needs depend on your individual metabolism, health status, medications, altitude and sweat rate. People with kidney disease, heart failure, or other conditions affecting fluid balance should follow their physician's specific recommendations. Does not replace professional medical or dietary advice.
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Frequently asked questions — Water Intake

How much water should I drink per day?
A common starting point is 35 mL per kilogram of body weight per day (about 0.5 fl oz per lb). A 70 kg (154 lb) sedentary adult needs roughly 2,450 mL (about 10 glasses). Active individuals and those in hot climates need significantly more — up to 4 L or more on intense-exercise days.
Does coffee count toward my daily water intake?
Yes, partly. Caffeinated beverages like coffee and tea do contribute to fluid intake, but caffeine has a mild diuretic effect. A useful rule of thumb: count black coffee or tea at about 75–80% of its volume toward your daily total. Herbal teas and fruit-infused water count fully.
How do I know if I am dehydrated?
Early signs of dehydration include a dry mouth, dark yellow urine, fatigue, headache, and reduced concentration. A practical check is the urine colour test: pale straw yellow means well-hydrated; dark amber or brown signals significant dehydration and requires immediate fluid intake.
Does water intake affect exercise performance?
Yes — even mild dehydration of 1–2% of body weight can impair aerobic performance, strength, and cognitive function. Drink 400–600 mL (14–20 fl oz) of water 2 hours before exercise, sip 150–250 mL every 15–20 minutes during activity, and rehydrate after with 1.5× the fluid lost through sweat.
Should I drink more water in summer?
Absolutely. Heat and humidity increase sweat rate, which can reach 1–2 L per hour during outdoor exercise. In hot or humid climates this calculator adds 300 mL to your baseline. In very hot conditions or during prolonged outdoor exercise, increase further and consider electrolyte replenishment to prevent hyponatremia.

📚 Learn more — official sources

🏛️ Organization WHO — Water and health World Health Organization resource on water, sanitation and health, including fluid requirements for different populations and climates. See official source → 🏛️ Organization National Academies — Dietary Reference Intakes for Water The US Institute of Medicine's Dietary Reference Intakes (DRIs) report, establishing Adequate Intake (AI) values for total water by age and sex. See official source → 🔬 Study Sawka et al. (2007) — Exercise and fluid replacement (ACSM) American College of Sports Medicine position stand on hydration during exercise, covering sweat rate, electrolyte losses and rehydration strategies. See on PubMed → 🏛️ Organization CDC — Water and healthier drinks Centers for Disease Control and Prevention page on daily water needs, benefits of hydration, and tips for increasing water intake. See official source →

About the Water Intake Calculator

Staying properly hydrated is one of the simplest performance and health levers available. The 35 mL/kg/day baseline used in this calculator aligns with widely referenced clinical nutrition guidelines. Activity and climate bonuses reflect increased sweat losses documented in exercise physiology literature — from roughly 500 mL extra on light training days to over 1,500 mL on days of intense effort in hot conditions.

The results are expressed in three practical formats — millilitres, standard 250 mL glasses, and US fluid ounces — and illustrated with a bottle-fill visual to make the target tangible. For a full body health picture, consider pairing this tool with our BMR, TDEE or macronutrient calculators.

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