Precision Utility
Water Intake
Calculator
Base Formula
35ml/kg
Output
Personalised
Work out your daily water intake in seconds. Enter your weight, activity level and climate — the calculator does the rest. You'll see your personalised target in litres, glasses and bottles, plus a visual breakdown to help you stay on track throughout the day.
Your Details
Daily Water Intake
2.98 L
Daily Litres
2.98 L
Glasses (250ml)
12
Bottles (500ml)
6
Extra for Activity
+350 ml
Daily Glasses (250 ml each)
12 glasses recommended
How the water intake calculator works
Start by entering your body weight in kilograms. The calculator uses the widely accepted 35 ml per kg formula as a baseline — so a 70 kg person needs roughly 2.45 litres before any adjustments.
Next, select your activity level. Exercise increases fluid loss through sweat, so the calculator adds between 350 ml (light exercise) and 1,000 ml (very intense training) to your daily target.
Finally, choose your climate. Warmer weather means more sweating and greater fluid loss, so the calculator adds 500–750 ml for warm and hot environments respectively.
Hit calculate and you'll see your personalised daily target in litres, the number of 250 ml glasses and 500 ml bottles you need, and a visual glass display to help you track your intake throughout the day.
What you need to know about hydration
Staying properly hydrated is essential for concentration, energy levels, digestion and kidney function. Even mild dehydration — losing just 1–2% of your body water — can impair mood and mental performance.
Key hydration facts from the NHS:
- The NHS recommends 6–8 glasses of fluid per day as a general guide, but individual needs vary
- Water, lower-fat milk, sugar-free drinks, tea and coffee all count toward your daily fluid intake
- You get roughly 20% of your daily water from food — especially fruit, vegetables and soups
- Dark yellow or strong-smelling urine is a key sign you need to drink more
- Older adults, pregnant women and people with certain medical conditions may need adjusted intake
Common signs of dehydration include thirst, dry mouth, tiredness, headaches, dizziness and dark urine. If you experience any of these regularly, try increasing your intake gradually.
You should drink more than usual when exercising, in hot weather, if you have a fever or illness causing vomiting or diarrhoea, or if you are pregnant or breastfeeding. Spread your intake evenly through the day rather than drinking large amounts at once.
Frequently asked questions
How much water should I drink a day?
A common guideline is around 2 litres per day, but your actual needs depend on your weight, activity level and climate. This calculator uses the 35 ml per kg formula as a baseline and adjusts for exercise and heat to give you a personalised daily target.
Does tea and coffee count towards my water intake?
Yes. The NHS confirms that tea, coffee, milk and sugar-free drinks all count towards your daily fluid intake. While caffeine has a mild diuretic effect, the water content in these drinks more than compensates.
What are the signs of dehydration?
Common signs include dark yellow urine, feeling thirsty, dry mouth, tiredness, dizziness and headaches. The NHS recommends checking your urine colour — pale straw is ideal. If it is dark or strong-smelling, you likely need to drink more.
Should I drink more water when exercising?
Yes. You lose fluid through sweat during exercise, so you need to drink extra to replace it. A good rule is to add 350–700 ml per hour of moderate to intense exercise. This calculator adjusts your total based on the activity level you select.
Can you drink too much water?
It is possible but rare. Drinking excessive amounts in a short period can cause hyponatraemia (low blood sodium), which can be dangerous. Spread your intake throughout the day and drink to thirst — there is no need to force large volumes at once.
How does climate affect water needs?
Hot or humid weather increases sweating and fluid loss, so you need to drink more. The calculator adds 500–750 ml per day for warm and hot climates respectively. Even in cooler UK weather, central heating and dry air can increase your fluid needs during winter.