A practical target is about 35 ml of water per kg of body weight from drinks — more for exercise and heat. Enter your details below. But the “8 glasses” rule is not evidence-based: food adds ~20%, coffee and tea count, and thirst and pale-yellow urine are the real guides.
Enter your weight for a practical daily water target.
Sweating a lot or drinking several litres? Replace electrolytes too — see the best electrolytes by cost per dose.
A practical starting point is about 35 ml per kg of body weight from drinks — roughly 2.5–3.5 L for most adults — plus more for exercise and hot weather. But there is no universal number: the National Academies set adequate TOTAL water (including food) at about 3.7 L/day for men and 2.7 L for women, and your body self-regulates. Let thirst and pale-yellow urine guide you rather than a fixed count.
No — it is a popular guideline, not an evidence-based requirement, and it ignores that about 20% of your water comes from food and that coffee and tea count too. Eight 8-oz glasses (~1.9 L) is fine as a rough habit for many people, but under- or over-shoots for others depending on size, activity and climate.
For normal daily hydration, water is enough. But if you sweat heavily, exercise for over an hour, or drink several litres, replacing electrolytes — mainly sodium and potassium — matters, because plain water alone can dilute them (rarely, dangerously, as hyponatremia). Add electrolytes for endurance, heat, or illness with fluid loss.
General information, not medical advice. Water needs rise with illness, pregnancy, breastfeeding and some medications, and certain heart or kidney conditions require fluid limits — follow your clinician’s guidance.