Overview
Water needs vary with body weight, activity, climate, food and health status. This tool gives a broad estimated range to avoid rigid rules and reminds you that excessive water can also be dangerous.
Formula
About 30–35 ml/kg for baseline needs, with additions for activity and climate. The result is shown in liters and cups.
How it works
Enter weight
A very precise weight is not needed; the estimate is broad.
Set activity and weather
Increase fluids with sweating or high heat.
Spread across the day
Drink with meals and around activity; avoid large amounts at once.
Worked examples
70 kg, no exercise, temperate
About 2.1–2.5 L/day from drinks and food.
70 kg, 60 minutes exercise, hot
About 2.9–3.7 L, adjusted for sweat and thirst.
Frequently asked questions
Should I always drink eight cups?
No. That rule is simplified; needs vary. Use thirst, urine and conditions as guides.
Do coffee and tea count?
Largely yes, although caffeine can slightly increase urine output. Water remains the main choice.
Can too much water be dangerous?
Yes. Drinking huge amounts quickly can cause low sodium. Do not force fluids.
Is it suitable for heart or kidney patients?
It is not a recommendation for them; a clinician sets the allowed fluid amount.
This calculator is for educational and informational purposes only and is not a substitute for professional advice.