How daily water intake is estimated
There is no single perfect number, but a widely used rule of thumb scales water needs with body weight. This calculator uses about 33 ml of water per kilogram of body weight as a baseline, then adds extra for activity:
baseline = weight(kg) × 33 ml
daily water = baseline + activity bonus
If you enter your weight in pounds, it is converted to kilograms first (1 lb = 0.4536 kg). The result is then expressed three ways: liters, US fluid ounces (1 L = 33.814 fl oz) and standard 8-oz cups.
Worked example
A 70 kg adult who exercises lightly a few days a week:
Baseline: 70 × 33 = 2,310 ml = 2.31 L.
Activity bonus (light): +350 ml.
Daily water: 2,660 ml ≈ 2.66 L ≈ 90 oz ≈ 11 cups.
Remember: roughly 20% of daily fluid comes from food, and other drinks count too. This figure is a target for total fluids, not just glasses of plain water.
What changes your needs
Hot or humid weather, high altitude, fever, pregnancy and breastfeeding all raise fluid needs. Larger bodies and more muscle also need more water. Use the estimate as a starting point and let thirst, along with pale-yellow urine, guide fine adjustments.