Hydration Calculator

Daily water intake by weight and gender

Hydration Calculator

Unit system

Gender

Recommendations are slightly higher for men on average.

Body weight

Enter your weight in kilograms (e.g. 70)

Your results

Enter your weight and gender to see your daily water intake.

Staying well hydrated supports energy, concentration, and bodily functions. This calculator estimates how much water to drink per day based on your body weight and gender. The result is a guideline; adjust for activity, climate, and health conditions.

How daily water intake is estimated

A common guideline is about 33 ml of water per kilogram of body weight per day. We apply a small gender factor (women slightly lower on average, in line with many dietary references).

\text{daily water (L)} = \text{weight (kg)} \times 0.033 \times \text{factor}

weight = body weight in kg; factor = 1 for men, 0.96 for women. Result in liters (L).

This includes total fluid from drinks and food. Increase intake in hot weather, with exercise, or if advised by your doctor.

Hydration tips

Simple habits to stay hydrated:

Drink a glass of water with meals and when you wake up.
Increase intake when exercising or in hot weather.
Thirst is a sign you may already be slightly dehydrated—sip regularly.
Water, milk, tea, and many foods (fruit, soup) all contribute to total fluid.
Carry a reusable bottle so you can sip throughout the day.
If you sweat a lot or exercise for over an hour, consider an electrolyte drink or a pinch of salt with water.
Drink before and during long meetings or travel.
Eat water-rich foods: watermelon, cucumber, oranges, and leafy greens.
Set gentle reminders if you often forget to drink.

Why hydration matters: physiology and biomechanics

Water is essential for almost every body function. Here's how it supports your physiology and movement.

Cells and tissues: Water makes up about 60% of adult body weight. It fills cells, carries nutrients and waste, and helps maintain cell shape and chemical reactions. Even mild dehydration can reduce cell volume and affect how well muscles and organs work.

Blood volume and circulation: Plasma is mostly water. When you're low on fluid, blood volume can drop, so the heart works harder to maintain blood pressure and deliver oxygen. That's why you may feel tired or light-headed when dehydrated.

Joints and connective tissue: Synovial fluid (which lubricates joints) and cartilage depend on adequate hydration. Good fluid intake helps keep joints moving smoothly and may reduce stiffness.

Temperature and sweat: You lose water through sweat to cool down. In hot weather or during exercise, drinking enough helps you keep a stable core temperature and avoid heat stress.

Cognition and mood: Studies link mild dehydration to poorer concentration, short-term memory, and mood. Staying hydrated supports alertness and mental performance.

Urine colour chart: a simple hydration check

Urine colour reflects how concentrated your urine is. Lighter usually means you're well hydrated; darker often means you need more fluid. Use this as a rough guide, not a medical test.

Pale straw or clear – well hydrated.
Light yellow – well hydrated.
Yellow – adequate hydration.
Dark yellow – drink more water soon.
Amber or honey – increase fluid intake.
Brown or very dark – drink water and consider speaking to a doctor if it persists.

Some foods (e.g. beetroot), supplements (B vitamins), or medicines can change urine colour. If you're unsure, ask a healthcare provider.

Frequently asked questions about hydration

How much water should I drink per day?

A common guideline is about 30–35 ml per kilogram of body weight per day, which this calculator uses. Needs vary with activity, climate, and health. Use the result as a starting point and adjust.

Does coffee or tea count toward my daily water intake?

Yes. Caffeinated drinks contribute to total fluid. Very high amounts of caffeine can have a mild diuretic effect, but moderate coffee or tea still counts.

What colour should my urine be if I'm well hydrated?

Pale yellow to light yellow is often a sign of good hydration. Very dark yellow or amber usually means you should drink more.

Can you drink too much water?

Yes. Excessive intake in a short time can dilute blood sodium (hyponatremia), which is rare but serious. Stick to sensible amounts and spread intake across the day; athletes in long events should follow evidence-based guidance.

When should I drink more than the calculator suggests?

Drink more when you sweat a lot (exercise, heat), when you're ill with fever or diarrhoea, when you're pregnant or breastfeeding (follow your doctor's advice), or in dry or high-altitude environments.

Do I need sports drinks or electrolytes?

For most daily activity and workouts under an hour, water is enough. For long or intense exercise, heavy sweating, or repeated sessions, electrolytes (sodium, potassium) can help. Use them when needed, not as a default.

Why do I feel thirsty at night?

Normal if you didn't drink enough during the day, slept with your mouth open, or ate a salty meal. Sipping water before bed is fine; drinking a lot right before sleep can wake you for the bathroom.

How do I know if I'm dehydrated?

Signs can include thirst, dark urine, dry mouth, tiredness, headache, or dizziness. In children and older adults, signs can be subtler. If you're worried, see a doctor.

Disclaimer

This calculator is for general information only. It does not replace medical or dietary advice. Individual needs vary with activity, health, and environment.

If you have a medical condition affecting fluid balance (e.g. heart or kidney disease), follow your doctor's guidance on how much to drink.

Rate This Calculator

Hydration tips

Simple habits to stay hydrated:

Drink a glass of water with meals and when you wake up.

Increase intake when exercising or in hot weather.

Thirst is a sign you may already be slightly dehydrated—sip regularly.

Water, milk, tea, and many foods (fruit, soup) all contribute to total fluid.

Carry a reusable bottle so you can sip throughout the day.

If you sweat a lot or exercise for over an hour, consider an electrolyte drink or a pinch of salt with water.

Drink before and during long meetings or travel.

Eat water-rich foods: watermelon, cucumber, oranges, and leafy greens.

Set gentle reminders if you often forget to drink.