Water Intake Calculator — How Much Water Should You Drink?
Use this free water intake calculator to find out exactly how much water you should drink each day. Enter your weight, activity level, climate and age range to get a personalised daily water recommendation in litres, millilitres and fluid ounces — plus exactly how many glasses and bottles that equals.
How Much Water Should You Drink Per Day?
The most widely used guideline for daily water intake is approximately 33ml of water per kilogram of body weight. A 70kg person would need around 2.3 litres per day under this formula — before adjusting for activity level.
The NHS recommends drinking 6–8 glasses of water per day (around 1.5–2 litres), but this varies by individual. Active people, those in hot climates, and pregnant or breastfeeding women will need more.
Daily Water Intake by Weight
Here's a quick reference for recommended daily water intake at different body weights at a moderate activity level:
| Body Weight | Water Per Day (litres) | Approx. Glasses (250ml) |
|---|---|---|
| 50 kg (110 lbs) | 1.98 litres | 8 glasses |
| 60 kg (132 lbs) | 2.38 litres | 10 glasses |
| 70 kg (154 lbs) | 2.77 litres | 11 glasses |
| 80 kg (176 lbs) | 3.17 litres | 13 glasses |
| 90 kg (198 lbs) | 3.56 litres | 15 glasses |
| 100 kg (220 lbs) | 3.96 litres | 16 glasses |
These figures are based on moderate activity. Increase by 10–20% for very active individuals or hot climates.
Factors That Affect Your Water Needs
Signs You're Not Drinking Enough Water
- Dark yellow urine — pale yellow or clear is the target
- Feeling thirsty — thirst is already a sign of mild dehydration
- Headaches and difficulty concentrating
- Dry mouth, lips or skin
- Fatigue or low energy levels
- Infrequent urination — less than 4 times per day suggests low intake
FAQs
How much water should I drink a day?
A general guideline is 33ml per kg of body weight — so a 70kg person needs around 2.3 litres per day. Active people and those in hot climates need more.
How many glasses of water should I drink per day?
Most adults should aim for 6–8 glasses (250ml each) per day, which is roughly 1.5–2 litres. Use the calculator above for a personalised recommendation based on your weight and activity level.
Does tea and coffee count towards daily water intake?
Yes — tea, coffee and other drinks count towards your daily fluid intake, despite being mild diuretics. Food also contributes around 20% of daily water needs.
What are signs of dehydration?
Dark yellow urine, thirst, headaches, dry mouth, fatigue and difficulty concentrating are all signs you need to drink more water.
Should I drink more water when exercising?
Yes — you lose 0.5–1 litre of fluid per hour of moderate exercise. Drink water before, during and after any workout.
Is this calculator free?
Yes completely free with no sign-up needed.