Water Intake Calculator
Calculate how much water you should drink daily based on your weight, activity level, and climate. Stay hydrated!
About this calculator
How much water do you need? A common starting point is about 33 ml per kilogram of body weight, adjusted up for exercise and for hot weather. This calculator applies an activity multiplier and a climate multiplier to your weight and tells you the daily total in litres and in glasses.
It also suggests how often to drink: spread across your waking day, a glass roughly every hour or so. About 20% of your intake comes from food, so drinking to the full total is not always necessary.
How to use it
- Enter your Weight and choose kg or lbs.
- Choose your Activity Level.
- Choose your Climate.
- Read the litres per day, the number of glasses and the drinking interval.
Formula
Litres = Weight(kg) × 0.033 × Activity factor × Climate factor. Activity factors run from 1.0 for sedentary to 1.8 for very active, and climate factors from 1.0 for temperate to 1.2 for hot weather. Glasses are counted at 250 ml.
Worked example
70 kg, with the default activity and climate settings
| Base need (33 ml per kg) | 2.31 litres |
| Adjusted total | 3.05 litres |
| Glasses of 250 ml | 13 |
If you sit in an air-conditioned office all day and do not exercise, 2.3 litres is a more realistic target.
This tool gives general information, not medical advice. Talk to a doctor or dietitian before making changes to your diet, exercise or medication.
Tips and common mistakes
- Pale yellow urine is the simplest sign that you are drinking enough.
- Tea, coffee, milk, soups, fruit and vegetables all count toward your fluid intake.
- Drink more in heat, when you exercise and when you have a fever.
- Do not force large volumes quickly. Sip steadily.
- People with kidney, heart or liver conditions may have fluid limits set by their doctor.
Frequently asked questions
How much water should I drink a day?
About 2 to 3 litres for most adults, depending on size, activity and weather.
Is 8 glasses a day a rule?
It is a rough guide. Your needs vary.
Do coffee and tea count?
Yes, they contribute to fluid intake.
Can you drink too much water?
Yes, though it is rare. Drinking extreme amounts quickly can lower blood sodium.
How do I know if I am dehydrated?
Dark urine, thirst, dry mouth, headache and fatigue.
Does food provide water?
Yes, about 20% of daily intake.