💧 Hydration
🆓 Free
Daily Schedule
💧 Water Intake Calculator
Calculate your personalised daily water intake based on body weight, activity level, climate, and special conditions like pregnancy, breastfeeding or illness. Get your target in litres and oz, an hourly drinking schedule, and a live tracker - plus the science behind hydration so you know exactly why each factor matters.
💧 Water Intake Calculator
Units
💡 This includes water from food (~20% of intake). Pure drinking water target shown separately below.
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liters / day
Total daily water need (incl. food)
⏰ Daily Drinking Schedule
Spread intake evenly through your day. Run calculator first.
Run the calculator first.
📊 Live Hydration Tracker
Tap to log water as you drink throughout the day. Resets when you reload the page.
Current intake
0% of goal
💧 Start logging water to see your hydration status!
📐 How Water Needs Are Calculated
Base Water Need (35ml per kg rule)
Adult water requirement:
Men: 35 ml × Body Weight (kg) = Total ml/day
Women: 31 ml × Body Weight (kg) = Total ml/day
In imperial units:
Adult: 0.5–1 oz per pound of body weight
Example: 70 kg adult male
Base water = 70 × 35 = 2,450 ml/day = 2.45 L
Note: This includes water from food (~20%)
Pure drinking water target: 80% of total
Activity & Exercise Adjustment
For every 30 minutes of exercise:
Add 350–500 ml (12–17 oz) water
For intense exercise (running, hot yoga, hiking):
Add 500 ml + 200 ml for every 30 min beyond first hour
Drink within 2 hours BEFORE exercise:
500 ml (17 oz)
During exercise:
150–250 ml every 15–20 min (5–8 oz)
After exercise:
500–750 ml per pound of body weight lost
Climate & Environmental Adjustments
Hot weather (over 25°C / 77°F):
Add 500 ml per 5°C above 22°C
Humid weather: add another 250–500 ml
High altitude (above 2,500m / 8,000 ft):
Add 500–750 ml (low humidity, increased breathing)
Air-conditioned indoor environment:
Slightly higher than humid outdoor air loss
(dry AC pulls moisture from skin)
Cold weather:
Surprisingly still increases needs by 5–10%
(respiratory water loss from cold dry air)
Special Conditions
Pregnancy: +300 ml/day (Institute of Medicine)
Breastfeeding: +700 ml/day
Fever: +400-500 ml per °C above normal
Vomiting/Diarrhea: +500-1000 ml as replacement
Caffeine intake: +200 ml per cup of coffee/tea
(mild diuretic effect)
Alcohol: +250 ml per drink (significant diuretic)
High-protein diet: +500 ml (kidney load)
High-fiber diet: +500 ml (fiber needs water)
❓ Frequently Asked Questions
AI Hydration Coach - Coming Soon!
AI-powered hydration reminders, personalised schedules and electrolyte balance recommendations based on your activity.
⏳ Coming Soon - Stay Tuned!
Water Intake Calculator - How Much Water You Actually Need and Why
The human body is approximately 60% water, and maintaining that balance is more nuanced than any fixed rule suggests. Water is involved in virtually every physiological process - regulating body temperature through sweat, transporting nutrients and oxygen, cushioning joints, removing waste through urine, and supporting the electrochemical processes that power every muscle contraction and nerve signal. Even mild dehydration - just 1–2% of body weight - measurably impairs cognitive function, mood, and physical performance.
Baseline formula this calculator uses: 35 ml per kg of body weight per day · Example: 70 kg person = 70 × 35 = 2,450 ml = 2.45 litres baseline · Then adjusted upward for activity (+0.5–1.5L), hot climate (+0.5–1L), pregnancy (+300ml), breastfeeding (+700ml), illness/fever (+500ml)
What Actually Determines Your Daily Water Needs
💪 Body & Activity Factors
- Body weight: Larger bodies contain more water and require more to replace losses. The 35ml/kg formula scales needs accurately across body sizes - a 100 kg person needs roughly 67% more water than a 60 kg person.
- Physical activity: Exercise increases sweat losses significantly. A moderate 60-minute workout can generate 0.5–1.5 litres of sweat depending on intensity and temperature. Hard training in heat can push losses to 2–3 litres per hour in extreme cases.
- Muscle mass: Muscle tissue holds significantly more water than fat tissue. Muscular individuals have higher baseline water requirements and also hold water more efficiently.
- Metabolic rate: Higher metabolism generates more heat, which the body dissipates through sweat - increasing water needs. This is why children have proportionally higher water needs per kg than adults.
🌡️ Environment & Health Factors
- Climate and temperature: Hot weather dramatically increases sweat losses even at rest. Working outdoors in 35°C heat requires 1–2 litres more per day than air-conditioned office work. High humidity reduces evaporative cooling, causing more sweating for the same temperature regulation effect.
- Altitude: High altitude (above 2,500m) increases respiratory water loss and urine output. Travellers to high-altitude destinations like Cusco, Lhasa, or the Himalayas should increase intake by 0.5–1 litre per day.
- Pregnancy: Blood volume increases 45–50% during pregnancy, requiring approximately 300ml extra per day. The amniotic fluid, foetal circulation, and increased kidney filtration all draw on maternal fluid reserves.
- Breastfeeding: Breast milk is approximately 87% water. Producing 700–900ml of milk per day requires an additional 700ml+ of fluid intake above baseline.
- Illness and fever: Each degree of fever above 37°C increases fluid losses by approximately 10%. Vomiting and diarrhoea can cause rapid, severe fluid and electrolyte losses.
Urine Colour - The Most Reliable Hydration Check
You do not need a calculator to check hydration status throughout the day - your urine colour tells you everything you need to know at a glance:
- Nearly colourless / very pale yellow: Possibly over-hydrated. Drinking too much water can dilute blood sodium - while rare, it warrants attention in endurance athletes.
- Pale yellow (like diluted lemonade): Well hydrated. Target zone for most of the day.
- Yellow: Adequately hydrated. Consider drinking a glass of water soon.
- Dark yellow: Mildly dehydrated. Drink water now - you are likely already experiencing mild performance and cognitive impairment.
- Amber / orange: Significantly dehydrated. Rehydrate immediately. Sustained amber urine warrants attention - it can indicate liver issues or severe dehydration.
- Brown or red: Drink water and seek medical attention. Can indicate serious dehydration, muscle breakdown (rhabdomyolysis), or other conditions.
Note: B-vitamin supplements (especially riboflavin/B2) cause bright yellow or fluorescent yellow urine regardless of hydration status - this is harmless and not a dehydration indicator.
Hydration for Exercise - Before, During and After
Exercise hydration follows a before-during-after protocol for best performance and recovery:
- Before exercise (2 hours prior): Drink 400–600ml (14–20 oz) of water. This pre-loads fluid stores and ensures you start the session in a well-hydrated state. Weigh yourself before and after if tracking sweat losses.
- During exercise: Drink 150–250ml (5–8 oz) every 15–20 minutes. Do not drink to thirst alone during high-intensity exercise - thirst sensation lags behind actual fluid needs. For sessions under 60 minutes, plain water is sufficient. For sessions over 60 minutes with heavy sweating, add electrolytes.
- After exercise: Rehydrate with 1.5 litres of fluid for every kilogram of body weight lost during the session. The 1.5× factor accounts for ongoing sweat and urine losses during the recovery window. Spreading rehydration over 4–6 hours after exercise improves absorption.
- Electrolytes for long sessions: Sweat contains sodium, potassium, chloride, magnesium, and calcium. For sessions longer than 90 minutes in heat, or any session producing very heavy sweat (visible salt deposits on skin), electrolyte replacement prevents hyponatremia and muscle cramping.
Hydration for Special Populations
- Children: Children dehydrate faster than adults relative to body size. EFSA recommendations: 1–3 years: 1.3 L/day; 4–8 years: 1.6 L; boys 9–13: 2.1 L; girls 9–13: 1.9 L; boys 14–18: 2.5 L; girls 14–18: 2.0 L. Active children and hot weather increase needs further. Children also have less reliable thirst sensation - scheduled water breaks are important during play and sport.
- Older adults (65+): Thirst sensation diminishes with age - older adults can be significantly dehydrated without feeling thirsty. Kidney function also declines, reducing the body's ability to conserve water. Scheduled drinking (a glass with each meal and at set times) is more reliable than drinking to thirst. Medications like diuretics increase losses further.
- Keto and low-carb diet: Glycogen (stored glucose) holds approximately 3–4 grams of water per gram. Transitioning to keto depletes glycogen stores, releasing significant amounts of stored water in the first 1–2 weeks. Ongoing ketosis also increases urinary electrolyte excretion (especially sodium). Aim for 3–4 litres daily on keto, plus extra sodium (approximately 3–5g/day).
- High-altitude travellers: Acclimatisation at high altitude increases both urination and respiratory water loss. Add 0.5–1 litre per day above baseline when at altitudes above 2,500m until acclimatised.