Sweat & sodium loss calculator.
Build a race-day hydration plan from a real 60-minute sweat test. Sport-specific intake guidance for runners and cyclists, plus sodium target.
Race-day hydration plan
- • Target intake: 800 ml/hr (≈70% of sweat rate)
- • Drink every 15-20 min: ~229 ml per sip
- • Sodium target: 889 mg/hr
- • Test weight dropped 1.3% — target keeping race-day loss under 2-3%
- ⚠️ High sweat rate — pre-hydrate the morning of and add a sodium-rich pre-load
Frequently asked
Why do a sweat test?
It removes the guesswork from hydration. A 60-min test tells you your actual sweat rate so you can plan fluid and sodium for race day instead of hoping.
How do I conduct one accurately?
Weigh nude (or in minimal dry clothing) before exercise, track every ml of fluid you drink for 60 minutes at race intensity, then weigh again toweled-dry in the same outfit. Weight lost + fluid consumed = sweat loss.
What's a normal sweat rate?
0.5-2.0 L/hr. Runners typically lose 15-30% more than cyclists at the same effort because of reduced airflow and higher core temp.
How much sodium during exercise?
Average loss 500-1200 mg/L. Target 400-800 mg/hr for most; salty sweaters and hot days can push 1000+ mg/hr.
Can I drink too much?
Yes — hyponatremia is real. Replace 60-80% of losses, not 100%. Let thirst guide and keep total weight loss under 2-3%.
VDOT calculator
Jack Daniels race predictor and training paces — the run pacing your hydration plan supports.
Heat & humidity pace calculator
Adjust marathon and half pace for temperature and humidity using heat index.
Carb-loading calculator
Race-week carbs by bodyweight and distance — pair fuel and fluid for the start line.
Hydration is solved. Now build the race plan.
Your sodium number means nothing without the workouts that test it. 1:1 coaching puts the bottle in the right hand at the right mile.
Boston-based · Trilingual EN/PT/ES · RRCA · USAT · TrainingPeaks L2 · 12× Boston qualifier