HYDRATION · SWEAT
Sweat Rate Calculator
Calculate your personal sweat rate from pre/post-exercise weigh-ins and estimate fluid and sodium losses using ACSM guidelines.
Result
Hydration metrics
Sweat rate, total fluid lost, and recommended hourly replacement.
Hydration status
Mild Dehydration
You lost 1.1% body weight. Mild dehydration can slightly reduce performance. Increase fluid intake by ~1050 mL/hr next session.
How to use it
- Open Sweat Rate Calculator and enter your current baseline accurately.
- Adjust one variable at a time so changes are easy to interpret.
- Review the headline output first, then inspect supporting metrics.
- Run at least one conservative and one aggressive scenario.
- Use outputs to set your next training or nutrition action for the week.
- Save or share this setup if you want to revisit it later, then check one easier and one harder version before you change your plan.
Questions people usually ask
What is sweat rate?
Sweat rate is the volume of fluid lost through sweating per hour of exercise, measured in litres/hour. Average endurance athletes sweat 0.5–2.5 L/hr; heavy sweaters can exceed 3 L/hr in heat.
Which formula is used?
The ACSM (American College of Sports Medicine) standard formula: Sweat Rate (L/hr) = (Pre-weight − Post-weight + Fluid consumed − Urine produced) / Duration in hours. Each 1 kg body weight loss equals approximately 1 litre of sweat.
How do I weigh myself accurately?
Weigh yourself nude immediately before exercise, then nude again immediately after — before eating or drinking anything post-exercise. Use the same scale both times.
Do I need to track urine output?
For most workouts under 90 minutes, urine output is negligible and you can leave it at 0. For ultra-endurance events, tracking urine output improves accuracy.
Why does sodium loss matter?
Sweat contains sodium (average ~920 mg/L). High sweat rates deplete sodium faster, risking hyponatremia in long events. If you lose more than 800 mg/hr, consider electrolyte drinks or salt tabs.
Is this tool free and private?
Yes. AI Fit Hub tools are free, browser-based, and no-signup. Your inputs stay in your browser.
Does this replace a sports dietitian?
No. These outputs are evidence-based estimates. For personalised hydration plans, especially for elite performance or medical conditions, consult a registered sports dietitian.
Formula
See the math
The underlying formula with variables defined, derivation shown, and a worked example with units.
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