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.
What does the Sweat Rate Calculator calculate, and which formula does it use?
The Sweat Rate Calculator computes fluid loss per hour with the ACSM/NATA weigh-in formula: sweat rate (L/hr) = (pre-exercise weight − post-exercise weight + fluid consumed − urine) ÷ hours exercised. It grades dehydration from percent body weight lost (thresholds at 1%, 2%, and 4%), recommends replacing about 80% of the sweat rate, and estimates sodium loss at 920 mg per liter of sweat.
Last updated:
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.
For agents
Use in an agent
Same math, same result shape as the UI above — as a static ES module. No HTTP request, no auth, no rate limit.
import { compute } from "https://aifithub.io/engines/sweat-rate-calculator.js";Contract: /contracts/sweat-rate-calculator.json Types: /engines/sweat-rate-calculator.d.ts Full agent guide →
Related Resources
Learn the decision before you act
Every link here is tied directly to Sweat Rate Calculator. Use the explanation, formula, examples, and benchmarks to pressure-test the calculator output from first principles.
Guide
6 MIN READHow to Stay Hydrated During Exercise
How to stay Hydrated During Exercise: optimize your performance and prevent dehydration during workouts with expert strategies, personalized fluid intake guid.
ReadFormula
6 VARIABLESMarathon Sweat Rate + Electrolyte Formula
Marathon hydration: sweat rate 0.5-2.5 L/h, sodium concentration 460-1840 mg/L. Casa 2007 + ACSM 2007 standards. Replace 70-90% of losses; avoid hyponatremia.
ReadExamples
4 EXAMPLESSweat Rate Examples
Discover practical sweat rate examples from athletes to industrial workers. Learn to calculate your fluid loss for personalized hydration, boosting health.
ReadChecklist
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Daily hydration checklist for athletes. Set fluid targets, drink on a schedule, monitor urine color, and stay ahead of training-day water and sodium needs.
ReadFormula
4 VARIABLESDaily Water Intake Formula
Daily water intake formula: water_ml = 30·mass_kg (sedentary) to 35·mass_kg (active). Add 350–500 ml/hour exercise. Food covers ~20%.
ReadExamples
4 EXAMPLESWater Intake Examples
Water intake examples: optimize your daily hydration with practical, data-driven examples.
ReadRelated deep dive
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Long-form context behind the calculator output.
- Pillar·10 min
Heat Acclimatization: Sodium and Plasma Volume
Heat acclimatization shifts plasma volume up 10-12% in 10-14 days. The sodium math that supports the adaptation and the workouts that drive it.
Read - Article·7 min
Marathon Sweat Rate: 70kg Runner, 2% Body Mass Loss in Warm Conditions
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Read - Pillar·11 min
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Heart-rate zone methods compared: Karvonen, %HRmax, %HRR, lactate threshold — accuracy by training age, error bands, and which one for which goal.
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