How it works
This calculator starts from a commonly used general guideline of about 30–35 mL of water per kilogram of body weight, then adds a fixed amount for elevated activity and for hot or humid conditions, both of which increase fluid loss through sweat.
base = weight (kg) × 33 mL
total = base + activity addition + climate addition
There is no single scientifically agreed figure for daily water needs — actual requirements vary by individual, diet (food itself provides a meaningful share of daily fluid), and health conditions. This is a general planning estimate, not a personal medical target. Anyone with a kidney, heart or other condition that affects fluid balance should follow their doctor's guidance instead.
Worked example
150 lb, moderate activity, temperate climate.
- Convert to metric: 150 lb = 68.04 kg.
- Base: 68.04 × 33 mL = 2.25 L.
- Add moderate activity: +0.35 L = 2.60 L.
- Climate off: +0 L.
A daily target of about 2.60 L, or roughly 11 cups.
Common questions
Does this include water from food and other drinks?
No — this is a target for direct fluid intake. Food, especially fruit and vegetables, contributes a meaningful share of daily water too, so this figure is intentionally a general planning number rather than a strict minimum you must drink on top of everything else.
Why does activity level change the target so much?
Sweat is the main extra source of fluid loss during exercise, and it scales with how hard and how long you're working. The activity addition here is a flat estimate for a typical session — genuine endurance training or heavy manual labor can call for considerably more.
Is drinking more water always better?
No. Drinking far beyond what your body needs can dilute blood sodium to dangerous levels (hyponatremia), particularly during prolonged intense exercise. This calculator gives a reasonable daily target, not a case for unlimited intake.