The ACSM exercise hydration protocol.
BEFORE
2 hours before
400–600ml
Pre-hydrate to start exercise well-hydrated
DURING
Every 15–20 min
150–350ml
Match sweat rate to prevent >2% body weight loss
AFTER
Within 2 hours
1.5× fluid lost
~750ml per lb of body weight lost through sweat
TIP: Drag the "Exercise Duration" slider to your daily workout time for an exercise-adjusted result
Your exercise-adjusted hydration intake.
STEP 01
Your profile.
Gender
Activity Level
Climate / Temperature
Enter your details
Your personalized hydration result will appear here.
Exercise hydration FAQ.
The American College of Sports Medicine (ACSM) provides the following general guidance for exercise hydration: drink approximately 400–600ml (14–22 oz) around 2 hours before exercise to begin well-hydrated; consume approximately 150–350ml (5–12 oz) every 15–20 minutes during exercise to match sweat losses; and after exercise, drink approximately 1.5 times the fluid lost (a practical estimate is around 750ml per pound of body weight lost) to support recovery. Our calculator adds approximately 500ml per 30 minutes of daily exercise to your baseline estimate, based on this general guidance. These are population-level estimates; actual sweat rates vary considerably between individuals.
For most exercise sessions lasting under 60 minutes at moderate intensity, plain water is generally sufficient for healthy adults. For longer or more intense sessions, particularly in hot conditions, sports drinks containing electrolytes (especially sodium and potassium) may help replace what is lost in sweat and may help prevent hyponatremia — a condition that can occur when large amounts of plain water are consumed during prolonged exercise. The threshold is not absolute; individual sweat rate, heat conditions, and intensity all influence when electrolytes become useful. If you exercise for more than 60–90 minutes, especially in heat, discussing electrolyte strategy with a sports dietitian or healthcare provider may be beneficial.
For endurance events such as marathons, general sports medicine guidance suggests aiming for approximately 400–800ml of fluid per hour, adjusted to your sweat rate and conditions. Drinking to thirst — rather than following a rigid schedule — is increasingly recommended by sports medicine experts, including ACSM, to reduce overhydration risk. For runs longer than 90 minutes, including sodium (via sports drinks or electrolyte supplements) is widely recommended to prevent dilutional hyponatremia. It is advisable to practise your hydration strategy during training rather than trying something new on race day. Individual needs vary considerably — consulting a sports dietitian for personalised advice is worthwhile for competitive events.