Hydrate Your Cells,
Ounces to Body Weight.
Free hydration calculators: daily water needs, sweat replacement for workouts, a personal sweat rate test, and a caffeine cutoff time.
Half Your Weight in Ounces
Baseline water needs start from 0.5 oz per pound of body mass before factoring climate or training.
Workout Sweat Rate
Pre vs post-workout weigh-ins convert fluid deficits directly into precise replenishment ounces.
Sodium & Electrolyte Balance
Prevent hyponatremia during long summer endurance sessions exceeding 90 minutes.
HydrateCheck Calculators
Daily Water Intake Calculator
A personalized daily fluid target from body weight, activity, and climate — with food and drink sources counted.
Workout Hydration Calculator
Pre, during, and post-workout fluid targets sized to session length and conditions — with the sodium question answered.
Sweat Rate Calculator
Your personal hourly sweat rate from the weigh-in test — the ground truth every hydration plan should use.
Caffeine Cutoff Calculator
When your last coffee should happen for a given bedtime — half-life math with a personal sensitivity adjustment.
Evidence-Based Physiology
The 8-glass rule was never about the water
Where the classic advice came from, what the actual science says, and the signals that beat any rule.
How to run a sweat-rate test that actually informs your racing
The weigh-in protocol, the math, and the two mistakes that corrupt it.
12 mistakes people make with hydration
The recurring errors we see in hydration — what causes each one, and the habit that prevents it.