Water Intake by Activity Calculator
A daily water target that adds fluid for the minutes you exercise on top of your body-weight baseline.
How it works
ounces = weight(lb) × 0.5 + 12 oz per 30 min of exercise
A practical hydration rule: drink about half your body weight in fluid ounces as a baseline, then add roughly 12 oz for each half hour of sweaty activity to replace what you lose. Food supplies another ~20% of daily fluid on top of this, and thirst plus pale-yellow urine remain the best day-to-day gauges.
Worked example
At 160 lb with 45 minutes of exercise: 160 × 0.5 = 80 oz baseline + (45 ÷ 30) × 12 = 18 oz → about 98 fl oz, roughly 2.9 liters or 12 cups.
Frequently asked questions
How much water should I drink when exercising?
Add about 12 oz (350 mL) per 30 minutes of activity on top of your baseline, and more in heat. For sessions over an hour of heavy sweating, include electrolytes, not just water.
Does this replace the 8-glasses rule?
It personalizes it. Eight 8-oz glasses (64 oz) is a rough average; scaling to body weight and activity fits an individual better, though all such rules are approximations.
Can I drink too much during exercise?
Yes — overdrinking plain water during long endurance events can dilute blood sodium (hyponatremia). Drink to thirst, spread intake out, and use electrolyte drinks for prolonged efforts.
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Educational estimate, not medical or dietary advice.