Sweat Rate Calculator
Find your hourly sweat rate from your before-and-after workout weight, then get a fluid replacement target tailored to you, with a dehydration risk flag. Works in metric and imperial units.
Sweat Rate Calculator
Units
Weigh-in
Weigh nude or in dry minimal clothing, towel off sweat first, same conditions both times.
Session details
Most people leave this at 0. Only fill it in if you took a bathroom break mid-session.
Rehydrate with
Replace 125 to 150% of fluid lost over the next few hours. Sip, do not gulp.
Drink during exercise (next time)
A practical in-session guide based on your sweat rate. Drink to thirst and keep intake under ~1.0 L/hr to avoid over-drinking.
Estimates only. Sweat rate shifts with heat, humidity, intensity, and acclimation, so measure across different conditions. This is exercise fluid loss, not a daily intake target. Talk to a clinician if you have a medical condition that affects hydration or sodium balance.
How to calculate your sweat rate
It is a simple routine, but the order matters. Weigh yourself right before the workout, nude or in dry minimal clothing, after toweling off. Do the same right after, wiping away any sweat first. Note anything you drank during the session and any bathroom breaks. Those four numbers (pre-weight, post-weight, fluid drunk, urine passed) are all you need.
The formula treats 1 kg of body mass change as roughly 1 L of fluid: sweat rate in L/hr equals pre-weight minus post-weight, plus fluid drunk, minus urine passed, all divided by the workout duration in hours. The calculator above normalizes everything for you and converts between metric and imperial with one toggle, so you can enter pounds and ounces or kilograms and liters.
What your sweat rate number means for hydration
A single L/hr figure does not mean much on its own, so the tool sorts it into bands: under 1.0 L/hr is low, 1.0 to 1.5 L/hr is moderate or typical, 1.5 to 2.0 L/hr is high, and over 2.0 L/hr is very high. Higher is not worse. It just means you have more fluid to plan for.
The number to actually watch is percent body weight lost. Studies put 2% as the point where dehydration starts to drag down performance and focus, which is why the calculator flags anything over 2% as a dehydration risk. Below 1% you are well hydrated, and 1 to 2% is a mild deficit worth topping up before your next session.
How much to drink to replace what you lost
Replace 125 to 150% of the fluid you lost, not just 100%, because you keep losing fluid through urine and sweat during recovery. In practical terms that is about 16 to 24 oz per pound lost. Spread it over the next few hours rather than drinking it all at once.
During exercise, treat your measured sweat rate as a ceiling, not a target to match drink-for-drink. Forcing fluid in can lead to over-drinking and, in rare cases, hyponatremia. For most people a workable in-session range is 0.4 to 1.0 L/hr, and drinking to thirst works fine. For a long workout or race, multiply your sweat rate by how long you expect to be out there to estimate total loss, then build a drink plan you can actually follow.
Track hydration through your 75-day challenge
Hydration is a daily task in challenges like 75 Tough and 75 Soft (the classic Drink Water habit, eight glasses a day). Once you know your sweat rate, that target stops being a guess: if you sweat buckets on training days, your water goal on those days should climb to match. Use this number to set a sensible per-day target, then log it every day. Reset75 handles the daily checklist, photos, and streak stats for free with no account required. Pair it with the gallon water tracker for the habit and the TDEE calculator for the bigger fitness picture, or jump straight into the 75 Tough tracker.
Frequently Asked Questions
Common questions about sweat rate calculator
What is a good sweat rate during exercise?
It varies a lot from person to person and day to day. As a rough guide: under 1.0 L/hr is low, 1.0 to 1.5 L/hr is moderate or typical, 1.5 to 2.0 L/hr is high, and over 2.0 L/hr is very high. None of these are good or bad on their own. They just tell you how much fluid you need to plan for.
How do I measure my sweat rate accurately?
Weigh yourself nude (or in dry, minimal clothing) right before your workout, after toweling off. Do the same right after, toweling off any sweat first. The weight difference plus anything you drank, minus any bathroom breaks, is your fluid loss. Divide by your workout time in hours to get your sweat rate.
How much water should I drink after a workout?
Replace 125 to 150% of the fluid you lost, since you keep losing some through urine and sweat during recovery. A common rule of thumb is 16 to 24 oz per pound lost. Sip it over the next few hours rather than gulping it all at once. Pair this with the water intake calculator for your daily baseline.
What does losing 2% of your body weight in sweat mean?
The 2% mark is roughly where dehydration starts to noticeably hurt your performance, focus, and how hard a session feels. This tool flags anything over 2% as a dehydration risk. Below 1% you are well hydrated, and 1 to 2% is a mild deficit worth topping up.
Should I replace 100% of the fluid I lose during exercise?
Not all at once during the session. Trying to match sweat loss drink-for-drink can lead to over-drinking and, in rare cases, hyponatremia (dangerously low blood sodium). Drink to thirst during exercise, then rehydrate gradually afterward to the 125 to 150% target.
What factors change my sweat rate?
Heat and humidity, how hard you go, your clothing and gear, body size, fitness level, and how used to the heat you are all move the number. That is why it pays to measure across different conditions rather than trust a single reading. A hot, hard session can easily double a cool, easy one.
Is sweat rate the same as how much water I should drink daily?
No. Sweat rate is the fluid you lose during exercise, not a daily intake target. Your daily needs include normal living, food, and other drinks on top of any workout losses. Use the water intake calculator or the gallon water tracker for your daily plan.
Can I use sweat rate to plan hydration for a race or long workout?
Yes. Multiply your sweat rate by the expected duration to estimate total loss, then build a realistic drink plan. Keep in-session intake in a practical range (roughly 0.4 to 1.0 L/hr for most people) and drink to thirst rather than forcing a fixed volume. Higher intensity sessions raise sweat rate, so the heart rate zone calculator can help you anticipate harder efforts.