How Much Do You Sweat per Hour?
A bathroom scale and your bottles are the only instruments. Enter the test numbers below.
Your Sweat Rate
Drinking to replace about 80% of sweat loss per hour is the planning target used in our hydration plan guide. Sweat is salty: on rides over two hours, add sodium with the fluid.
How It Works
Weight lost plus fluid drunk is the sweat you made. Divide by the hours and you have a rate.
The Formula
Sweat loss = (weight before - weight after) + fluid drunk - urine Sweat rate (per hour) = sweat loss / ride time in hours Drinking target (per hour) = sweat rate x 0.80 Body weight lost (%) = (weight before - weight after) / weight before x 100The method treats every gram of weight you lose on the bike as sweat, after adding back what you drank and subtracting anything you passed. A liter of sweat weighs a kilogram, which is why the metric version of the test is easier: the scale and the bottle use the same unit. In US units a pound of sweat is about 15.3 fluid ounces. The calculator converts for you either way.
Breath loses a little water too, and the body makes a little from burning fuel, but over a one-hour test they roughly cancel and the simple method is what sports science labs use in the field.
Running a Clean Test
Weigh in dry, in the same kit, before and after. Ride about an hour at the effort and in the weather you want to plan for. Towel off before the second weigh-in, because sweat on the skin still weighs something. Skip the test if you need a bathroom stop you cannot measure. Then do it again in a different season: the rider who sweats 0.7 liters an hour in April often sweats 1.5 in July.
A Worked Example
A rider weighs 170.0 lb before a one-hour ride and 168.4 lb after, having drunk a 24 oz bottle. Weight lost: 1.6 lb, about 0.73 liters. Add the 24 oz (0.71 liters) drunk and the hour's sweat was 1.44 liters, about 48.5 oz. The drinking target is 80% of that, 39 oz an hour, or a bottle and two thirds. On this ride the 24 oz drunk fell short, so the rider finished 0.9% lighter. Under 2% is fine; past 2% performance drops.
Why 80%, Not 100%
Replacing every ounce is hard to drink and unnecessary; the goal is to finish within 2% of starting weight. Drinking more than you sweat is the real danger on a long day, because plain water in excess dilutes blood sodium. Sweat carries sodium out at anywhere from 200 to 2,000 mg per liter, so on rides past two hours put some of it back with an electrolyte mix. The full plan, including pre-ride and recovery drinking, is in how to calculate sweat rate and build a hydration plan; the heat side is in beating the heat on the bike.
Frequently Asked Questions
- How do I run a sweat rate test on the bike?
- Weigh yourself nude or in dry kit right before a ride, ride for about an hour at your usual effort in the conditions you want to plan for, and weigh in again after toweling off. Weigh your bottles before and after, or note how much you drank. Enter the four numbers here. Repeat the test in different weather, because sweat rate on a hot afternoon can be double the cool-morning figure.
- How much should I drink per hour on a ride?
- Aim to replace about 80% of what you sweat each hour, which for a typical rider losing 1 liter an hour is around 27 oz, a little more than one standard bottle. Drinking less than that lets dehydration build over a long ride; drinking more than you sweat risks diluting your blood sodium. The calculator turns your own sweat rate into ounces per hour and bottles per hour.
- What counts as a normal sweat rate for cyclists?
- Most riders sweat between 0.5 and 2 liters an hour, with 1 liter an hour a common figure in warm weather at a steady effort. Heat, humidity, intensity, body size, and fitness all push it up: well-trained riders start sweating sooner and sweat more. A rate above 2 liters an hour is unusual and calls for a planned sodium strategy as well as fluid.
- Should I weigh myself before and after every ride?
- A handful of tests, one per season and one per type of ride, gives a usable plan without turning every ride into a lab session. Weigh in again when conditions change: the first hot week of summer, a trip to a humid climate, or a jump in training intensity. Keep the results in a note on your phone and the drinking plan takes care of itself.
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