Free tool
Daily water intake calculator
Enter your body weight, activity level and climate. The tool estimates how much water to drink a day, in litres and glasses, using the commonly cited 30 to 35 ml per kg guide with adjustments for exercise and heat. Nothing you type is stored or sent anywhere.
Your result
This is a general estimate from a standard formula, not medical advice and not a diagnosis. It does not account for health conditions, pregnancy, medication or how much water you already get from food. Consult a doctor for a fluid intake target suited to you.
How this estimate is calculated
The formula adds three parts together: a baseline from your body weight, an add-on for activity level, and an add-on for climate.
| Part | How it is estimated |
|---|---|
| Baseline | About 33 ml per kg of body weight, the midpoint of the commonly cited 30 to 35 ml/kg guide. |
| Activity add-on | 0 ml for little to no exercise, up to 800 ml a day for intense daily exercise or a physically active job. |
| Climate add-on | 0 ml in normal weather, about 500 ml in hot or humid weather to cover extra sweat loss. |
Common questions
How much water should I drink a day?
A commonly cited general guide is about 30 to 35 ml of water per kilogram of body weight per day. For a 65 kg adult that works out to roughly 2 to 2.3 litres before accounting for exercise or hot weather. This tool uses the midpoint of that range and then adds a fixed amount for your activity level and climate.
Does exercise increase how much water I need?
Yes. Sweat loss during exercise adds to your fluid needs on top of your baseline. This tool adds an estimated 300 to 800 ml depending on how much you selected for activity level, from little to no exercise up to intense daily exercise or a physically active job. Longer or more intense sessions can need more than this general estimate covers.
Does hot or humid weather change how much water I need?
Yes. Heat and humidity increase sweat loss even without exercise, so this tool adds roughly 500 ml on top of your baseline when you select a hot or humid climate. People who work outdoors in heat, or during a heatwave, often need more than this general add-on.
Is this number exact for me?
No. This is a general estimate from a standard formula, not medical advice and not a diagnosis. Actual fluid needs vary with health conditions, pregnancy, medication, body composition and how much water you already get from food. If you have a kidney, heart or other condition affecting fluid intake, or you are pregnant or breastfeeding, talk to a doctor about the right amount for you.
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