Sweat Rate Calculator
Fluid lost per hour, and what to drink back.
Enter your values
Enter the weight before in lb.
Enter the weight after in lb.
Enter the fluid drunk during in oz.
Enter the duration in hours.
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
- 40 oz per hour
- Total fluid lost
- 60 oz
- Rehydrate with (150% of loss)
- 60 oz
- Body weight lost
- 1.47%
Quick answer
Sweat rate is pre-exercise weight minus post-exercise weight, plus fluid drunk, divided by hours exercised.
Sweat rate = (weight lost + fluid drunk) ÷ hours
At a glance
| What it does | Fluid lost per hour, and what to drink back. |
|---|---|
| Category | Health |
| Inputs needed | Weight before, Weight after, Fluid drunk during, Duration |
| Main output | Sweat rate |
| Formula | Sweat rate = (weight lost + fluid drunk) ÷ hours |
| Cost | Free — no sign-up, no download |
How to use the Sweat Rate Calculator
- 1Weigh yourself before training with minimal clothing.
- 2Track fluid drunk during the session.
- 3Weigh again afterwards and enter the numbers.
Inputs explained
- Weight before(lb)
- Enter the weight before in lb.
- Weight after(lb)
- Enter the weight after in lb.
- Fluid drunk during(oz)
- Enter the fluid drunk during in oz.
- Duration(hours)
- Enter the duration in hours.
Worked example
Using the values the calculator loads with:
Inputs
- Weight before170 lb
- Weight after167.5 lb
- Fluid drunk during20 oz
- Duration1.5 hours
Results
- Sweat rate40 oz per hour
- Total fluid lost60 oz
- Rehydrate with (150% of loss)60 oz
- Body weight lost1.47%
Frequently asked questions
What loss is dangerous?
Above 2% of body weight, performance drops measurably; above 4% raises heat illness risk sharply.
Why drink 150% of loss?
Some of what you drink is excreted rather than retained, so replacing 1.5× the deficit fully restores fluid balance.
What do I need to enter into the Sweat Rate Calculator?
Just 4 values: weight before, weight after, fluid drunk during, 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 Sweat Rate Calculator work out the answer?
Sweat rate is pre-exercise weight minus post-exercise weight, plus fluid drunk, divided by hours exercised. 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 Sweat Rate 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.