# Hydration Sweat Rate Calculator Calculate sweat rate, net fluid loss, and a recommended hourly drinking range from pre/post body weight, fluid intake, urine volume, and session duration. > Canonical page: https://elysiatools.com/en/tools/hydration-sweat-rate-calculator - **Category:** Health - **Keywords:** sweat rate, hydration calculator, fluid loss, dehydration, runners, triathlon, electrolytes, hourly fluid intake ## Overview fluid_loss (L) = (pre − post) kg + intake L − urine L; sweat_rate = fluid_loss ÷ hours; hourly range ≈ 80–110% of sweat rate. ## Inputs - **Pre-exercise body weight** (number): e.g. 70 - **Post-exercise body weight** (number): e.g. 68.5 - **Weight unit** (select) - **Fluid intake during session** (number): e.g. 500 - **Urine volume during session** (number): e.g. 0 - **Fluid unit** (select) - **Exercise duration (minutes)** (number): e.g. 90 - **Decimal places** (number) ## When to use - When planning a hydration strategy for long-distance endurance events like marathons or triathlons. - After completing a training session in hot or humid conditions to assess fluid loss and recovery needs. - When adjusting fluid intake protocols across different seasons or environmental temperatures. ## How it works - Input your body weight measured immediately before and after your exercise session. - Enter the total volume of fluids consumed and any urine volume excreted during the workout. - Specify the duration of the exercise session in minutes and select your preferred units of measurement. - The calculator computes your net fluid loss, sweat rate per hour, and a recommended hourly drinking range representing 80% to 110% of your sweat rate. ## Use cases - Calculating sweat rate during summer running sessions to adjust handheld bottle capacity. - Establishing baseline hydration targets for triathletes preparing for long-distance races. - Monitoring fluid loss variations between indoor cycling trainer sessions and outdoor rides. ## Frequently asked questions ### How is sweat rate calculated? It is calculated by subtracting post-exercise weight from pre-exercise weight, adding fluid intake, subtracting urine volume, and dividing the total by the exercise duration in hours. ### Why does the calculator recommend an hourly drinking range of 80% to 110%? This range helps replace lost fluids effectively during exercise while preventing overhydration or excessive dehydration. ### Can I use imperial units like pounds and fluid ounces? Yes, you can select pounds (lb) for weight and fluid ounces (fl oz) for fluid intake and urine volume. ### Why should I track urine volume during a workout? Tracking urine volume ensures that fluid loss calculations isolate sweat loss rather than general fluid excretion. ### What is a safe percentage of body mass loss during exercise? It is generally recommended to keep body mass loss under 2% to avoid performance decrements and dehydration symptoms. ## Related tools - [Blood Alcohol Content (BAC) Estimator](https://elysiatools.com/en/tools/bac-calculator): Estimate your BAC from sex, weight, drinks and time using the Widmark formula. Returns g/dL and ‰, predicts sober time, and flags the impairment tier and legal driving limits. - [Carrying Capacity Estimator (Fit K from Time-Series Data)](https://elysiatools.com/en/tools/carrying-capacity-estimator): Least-squares logistic fit of K, r, t₀ from `time, population` observations, with fitted curve, residuals, and plateau warnings. - [Fetal Development Timeline (by Gestational Week)](https://elysiatools.com/en/tools/fetal-development-timeline): See week-by-week fetal development from conception to birth (40 weeks). 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