Sweat rate calculator
Sweat rate = (weight before − weight after + fluid drunk − urine) ÷ hours. One kilo of lost body weight is about one litre of sweat. Weigh yourself before and after a ride of an hour or more, enter what you drank, and you get your sweat rate, your fluid deficit and a drinking target for race day.
Hours:minutes:seconds
- Total sweat loss: 1.65 L
- Body weight lost: 1.2 % Acceptable
- You replaced 45 % of what you sweated
On a similar day, aim for about 850 mL per hour
Plan race fueling with this sweat rateSweat rate = (weight before − weight after + fluid drunk − urine) ÷ hours. 1 kg ≈ 1 L.
How to calculate your sweat rate
Your sweat rate is how much fluid you lose per hour through sweat. The simplest accurate way to measure it needs only a bathroom scale:
Sweat rate (L/h) = (weight before − weight after + fluid drunk − urine) ÷ hours
One kilogram of body weight lost during exercise is almost exactly one litre of sweat. Adding back what you drank, and subtracting what you passed as urine, gives your total sweat loss. This calculator is part of the free LeCoach cycling calculators.
How to do a sweat test
- Pee, then weigh yourself with as little clothing as possible, on the same scale you will use afterwards.
- Ride or run for at least an hour, ideally at race-like effort and in conditions similar to your event.
- Note everything you drink. Weigh or measure your bottles before and after.
- Do not pee during the session if you can avoid it. If you do, estimate the volume.
- Towel off and weigh yourself again, in the same clothing as before (or none). Wet kit adds weight that is not your body.
- Enter the numbers in the calculator.
Repeat the test in different conditions: a cool day, a hot day, an indoor session. Your sweat rate can easily double between them, and indoor riding without strong airflow often produces the highest rates of all.
What your result means
| Body weight lost | What it means |
|---|---|
| Under 1 % | Well hydrated. You drank close to what you lost. |
| 1–2 % | Acceptable for most sessions and races |
| Over 2 % | Performance likely suffers, especially in heat and longer events |
| Weight gained | You drank more than you sweated. Drink less next time. |
Typical sweat rates for endurance athletes run from about 0.5 to 1.5 litres per hour, and can reach 2 litres or more in heat. Neither a high nor a low sweat rate is better; it is simply how your body works. What matters is that your drinking plan fits it.
Want this worked out for you every day? LeCoach builds your training around your own numbers.
Try LeCoach for freeFrom sweat rate to a drinking plan
You do not need to replace every drop. A practical target is about 75 % of your sweat losses, between 400 and 1,000 mL per hour. For the example rider with 1.10 L per hour, that is about 850 mL per hour on a similar day.
Two warnings:
- Do not drink more than you sweat. Over-drinking, especially plain water, can lower your blood sodium (hyponatremia). It is rare, but it is dangerous, and it happens most to slower athletes in long events who drink at every opportunity.
- Sodium matters too. Sweat contains sodium, on average a little under 1,000 mg per litre, but ranging from a few hundred to over 2,000 mg per litre between people. If you sweat a lot and see white salt marks on your kit, use a drink with more sodium.
To turn this into a race plan with carbs and sodium as well, use the button above to send your sweat rate to the race nutrition calculator.
Common mistakes
- Weighing in wet kit. Sweat-soaked kit can hold several hundred grams. Weigh without it or in dry kit both times.
- Measuring on a short session. Under about 45 minutes, small scale errors make the result unreliable.
- Using one test for every condition. A cool spring ride and a hot summer race are completely different. Test in conditions like your event.
- Using a cheap scale with 0.5 kg steps. You need a scale that reads to 0.1 kg.
- Not counting what you spat out or poured over your head. Only count what you swallowed.
When your sweat rate changes
- Heat acclimation increases sweat rate over 10 to 14 days of training in heat. That is a good thing: you cool better, but you need to drink more.
- Intensity: harder efforts produce more heat and more sweat.
- Humidity: sweat evaporates less, so you cool less efficiently and may sweat more.
- Fitness: fitter athletes tend to start sweating earlier and sweat more.
For more on fluids and electrolytes, read our guide to hydration and electrolytes for cyclists and cycling hydration: how much, when and what works.
You can ask LeCoach how much to drink on your next long ride, and it answers from the planned workout's duration and intensity.
Sources
- Sawka MN et al. American College of Sports Medicine position stand: exercise and fluid replacement. Medicine and Science in Sports and Exercise, 2007;39(2):377-390.
- Baker LB. Sweating rate and sweat sodium concentration in athletes. Sports Medicine, 2017;47(Suppl 1):111-128.
- Hew-Butler T et al. Statement of the Third International Exercise-Associated Hyponatremia Consensus Development Conference. Clinical Journal of Sport Medicine, 2015;25(4):303-320.
Frequently asked questions
How do I calculate my sweat rate?
Weigh yourself before and after a session of at least an hour, add the fluid you drank, subtract any urine, and divide by the hours. Losing 0.9 kg while drinking 0.75 L in 90 minutes is a sweat rate of 1.65 ÷ 1.5 = 1.1 litres per hour.
What is a normal sweat rate?
For endurance athletes, about 0.5 to 1.5 litres per hour is typical, rising to 2 litres or more in heat or during hard efforts. There is no ideal number; what matters is matching your drinking to your own rate.
How much should I drink per hour based on sweat rate?
About 75 % of your sweat rate, within 400 to 1,000 mL per hour, is a sensible target. That keeps body weight loss under about 2 % without the risk of over-drinking. A rider sweating 1.1 litres per hour would aim for around 800 to 850 mL.
Is losing 2 % of body weight bad?
Up to about 2 % is generally tolerated well. Beyond that, endurance performance tends to drop, especially in heat. Losing more than 3 to 4 % increases the risk of heat illness. In cool conditions and short races, the effect is smaller.
Why do I sweat so much indoors?
On a trainer there is no airflow to evaporate sweat and carry heat away, so your body produces more sweat to cool down. One or two strong fans make a big difference to both comfort and power.
Does sweat rate change with fitness?
Yes. Fitter, heat-acclimated athletes usually sweat more and start sweating earlier, because their cooling system works better. Retest your sweat rate after a summer of training.
More questions about drinking and fueling?
Ask LeCoach about fluid, fueling or weight, and it answers from your actual training load, not generic rules.
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