Use this calculator to understand how much fluid and minerals you lose in sweat. The idea is to weigh yourself before and after exercising in a controlled way (no drinking, no eating, no peeing between weigh-ins). The weight difference therefore is the amount of fluid lost in sweat.
|Sweat (lbs)||0 lbs||0 lbs/hr||0 lbs/mi|
|Sweat (ozs)||0 ozs||0 ozs/hr||0 ozs/mi|
|Sweat (liters)||0 liters||0 liters/hr||0 liters/mi|
|Sodium||0 mg||0 mg/hr||0 mg/mi|
|Potassium||0 mg||0 mg/hr||0 mg/mi|
|Calcium||0 mg||0 mg/hr||0 mg/mi|
|Magnesium||0 mg||0 mg/hr||0 mg/mi|
The figures above are "typical". If you are acclimated to heat, then you will likely lose less sodium. If you are not acclimated and are running hard in hot weather, you may lose more.
Losing more than a couple grams of sodium can lead to cramping and worse. Eat salty foods along the way or take salt / electrolyte capsules periodically to maintain a healthy salinity.