Water Intake Calculator
Find out exactly how much water you should drink based on your weight, activity, and climate.
Your Details
Your Daily Water Target
Spread it through the day
Enter your weight above to see your daily water target.
Frequently Asked Questions
How much water should you drink a day?
Hydration affects almost every system in your body — from regulating body temperature and lubricating joints to transporting nutrients and flushing waste. Yet the famous "8 glasses a day" rule has no scientific basis. Your actual needs depend on your body size, how active you are, and where you live.
The most widely used formula comes from the European Food Safety Authority (EFSA) and the US National Academies, which both recommend roughly 35 ml per kg of body weight as a daily baseline for a sedentary adult in a temperate climate. A 70 kg person therefore needs around 2,450 ml (2.45 litres) per day at rest — already more than 8 standard 240 ml glasses.
Physical activity significantly raises this number. Even a moderate 45-minute workout can cause sweat losses of 400–700 ml. Athletes training twice a day in hot conditions can easily need 4–5 litres total. The calculator above accounts for activity level with a tiered adjustment so you're not under-fuelled.
Signs of dehydration — and how to catch it early
Mild dehydration (1–2% body weight)
- Thirst and dry mouth
- Darker yellow urine
- Reduced concentration
- Slight headache
Moderate–severe dehydration (3–5%+)
- Fatigue and dizziness
- Muscle cramps
- Rapid heartbeat
- Significant strength loss
The simplest monitoring tool is urine colour. Pale straw yellow = well hydrated. Dark amber = drink more. Completely clear = you may be overhydrating.
Daily hydration tips that actually work
Start the day with water
Drink a full glass (250–500 ml) immediately on waking. You lose water overnight through breathing, and replenishing first thing kickstarts metabolism and reduces hunger.
Drink before meals
A 500 ml glass 20–30 minutes before each meal helps digestion, reduces caloric intake, and contributes a significant chunk of your daily target with no extra effort.
Use reminders
Set hourly phone reminders or use a marked water bottle to track intake throughout the day. Out of sight, out of mind applies strongly to hydration habits.
Eat water-rich foods
Cucumber (96% water), watermelon (92%), strawberries (91%), and lettuce (95%) all contribute to hydration. Food accounts for roughly 20% of most people's daily water intake.
Hydrate around exercise
Drink 400–600 ml 2 hours before exercise, sip 150–250 ml every 15–20 minutes during, and rehydrate with 500 ml per 0.5 kg of body weight lost afterwards.
Adjust for climate
In hot or humid environments, increase intake by 10–20% minimum. Air-conditioned offices are surprisingly dehydrating too — the low humidity causes imperceptible moisture loss.
Water intake by weight — quick reference chart
Baseline values for a sedentary adult in a temperate climate (35 ml/kg). Add 200–900 ml for activity and 200–400 ml for warm/hot climates.
| Body weight | Daily water (ml) | In litres | Cups (240 ml) |
|---|---|---|---|
| 50 kg / 110 lbs | 1,750 ml | 1.75 L | 7 cups |
| 60 kg / 132 lbs | 2,100 ml | 2.1 L | 9 cups |
| 70 kg / 154 lbs | 2,450 ml | 2.45 L | 10 cups |
| 80 kg / 176 lbs | 2,800 ml | 2.8 L | 12 cups |
| 90 kg / 198 lbs | 3,150 ml | 3.15 L | 13 cups |
| 100 kg / 220 lbs | 3,500 ml | 3.5 L | 15 cups |