Hydration Calculator: Water for Exercise and Hot Weather
Enter your weight, exercise time and how hot it is to see your total drinks for the day. Weigh yourself before and after exercise for a personal sweat rate.
- Nothing you type is stored
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Total drinks today
2.3L
- Base
- 1.8 L
- For exercise
- 0.5 L
An estimate for general information, not medical advice.
Sip through the day rather than all at once.
How to use
- Enter your weight and exercise minutes.
- Choose how hard you work and how hot it is.
- Optionally add weights before and after exercise for your sweat rate.
Good to know
Base drinks = 35 ml/kg × 80% (the rest comes from food). Exercise adds about 0.4, 0.7 or 1.0 L per hour for light, moderate or hard work; the ACSM position stand (2007) reports sweat rates of about 0.3–2.4 L an hour. Heat adds 0.5 L (hot) or 1.0 L (very hot) a day, a rule of thumb for Indian summers.
Sweat test: weigh before and after exercise in light clothing. Sweat rate = (weight before − after + fluid drunk) ÷ hours. Afterwards, drink about 1.5 L per kg lost (ACSM: 1.25–1.5 L/kg). Losing more than 2% of body weight hurts performance.
For long sweaty sessions or heat-wave days, add salt with drinks (nimbu-pani with a pinch of salt, ORS, buttermilk). Dizziness, confusion or no sweating in heat are emergencies. Fluid-restricted patients must follow their doctor.
Questions
How much water should I drink when exercising?
Roughly 0.4–1 L for each hour, depending on effort and heat. A sweat test gives your own number.
How much extra water in summer?
About 0.5–1 L more a day in hot weather, more if you work outdoors.
Should I drink ORS after exercise?
For sessions over an hour with heavy sweating, or on very hot days, drinks with some salt help. Plain water is fine for short workouts.
How do I know I am dehydrated?
Thirst, dark urine, headache and tiredness. Weight loss of more than 2% after exercise also points to it.
Is my data stored?
No. Everything is calculated on your device.