Health
How Much Water You Actually Need Per Day
Morecalcs Team 2026-07-18· 5 min
The 8×8 rule has no science. Here's a better formula.
The old rule
"Eight 8-oz glasses" traces to a 1945 recommendation that included water from food, which most people forget to subtract.
A better estimate
30–35 ml per kg of body weight, plus 500 ml per hour of hard exercise. A 70 kg lifter doing a 1-hour session needs about 2.6 L total.
Signs you're behind
Dark yellow urine, headaches, low energy. Thirst is a late signal.
Overhydration is real
Chugging 4+ liters in a short window can dilute sodium dangerously (hyponatremia). Sip, don't gulp.
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