Exercise Hydration Calculator
Fluid to drink per hour from your sweat rate.
Enter your values
Enter the weight before in kg.
Enter the weight after in kg.
Enter the fluid drunk in ml.
Enter the duration in h.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- Sweat rate
- 1,200 ml/hour
- Total fluid lost
- 1,800 ml
- Drink during exercise
- 960 ml/hour
- Post-session replacement
- 2,700 ml
Quick answer
Sweat rate is weight lost during exercise plus fluid drunk, divided by hours. Replace 100-150% of losses afterwards.
sweat rate = (weight lost + fluid drunk) / hours
At a glance
| What it does | Fluid to drink per hour from your sweat rate. |
|---|---|
| Category | Fitness |
| Inputs needed | Weight before, Weight after, Fluid drunk, Duration |
| Main output | Sweat rate |
| Formula | sweat rate = (weight lost + fluid drunk) / hours |
| Cost | Free — no sign-up, no download |
How to use the Exercise Hydration Calculator
- 1Weigh yourself without clothes before and immediately after a session.
- 2Record everything you drank during it.
- 3Aim to lose no more than 2% of body weight per session.
Inputs explained
- Weight before(kg)
- Enter the weight before in kg.
- Weight after(kg)
- Enter the weight after in kg.
- Fluid drunk(ml)
- Enter the fluid drunk in ml.
- Duration(h)
- Enter the duration in h.
Worked example
Using the values the calculator loads with:
Inputs
- Weight before74.5 kg
- Weight after73.2 kg
- Fluid drunk500 ml
- Duration1.5 h
Results
- Sweat rate1,200 ml/hour
- Total fluid lost1,800 ml
- Drink during exercise960 ml/hour
- Post-session replacement2,700 ml
Frequently asked questions
Do I need electrolytes?
Above one hour of hard sweating, sodium replacement helps absorption and prevents cramping.
Can I drink too much?
Yes — hyponatraemia is dangerous. Do not drink beyond your sweat rate.
What do I need to enter into the Exercise Hydration Calculator?
Just 4 values: weight before, weight after, fluid drunk, duration. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Exercise Hydration Calculator work out the answer?
Sweat rate is weight lost during exercise plus fluid drunk, divided by hours. Replace 100-150% of losses afterwards. It applies the formula sweat rate = (weight lost + fluid drunk) / hours and shows the working so you can check each step by hand.
Is the Exercise Hydration Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.