Cycling hydration

Weigh yourself before and after a ride to find your sweat rate and how many bottles your next ride needs.

Your details

Sweat rate

0.94 L

an hour

Body weight lost on the test ride1.2%
Sweat lost on the test ride1.41 L
Next ride of 3 hr: drink at least1,290 ml
and no more than2,814 ml
Bottles of 750 ml1.7 to 3.8
Every 20 minutes (9 times)143 to 313 ml

The aim is to lose less than 2% of your body weight without ever finishing heavier. Sweat rate changes with heat, effort and fitness, so repeat the test in summer and winter. Weigh in the same kit, towelled dry.

Dizziness, confusion or stopping sweating in the heat is an emergency: stop, cool down and call 999.

The working

12 st 0 lb to 11 st 12 lb over 90 minutes

You lost 0.91 kg and drank 0.5 litres, so you sweated about 1.41 litres: 0.94 litres an hour, and 1.2% of your weight came off. For a 3 hour ride, drink at least 1.29 litres to stay under 2% loss, and no more than 2.81 litres.

Doing the test

Get a clean number

Weigh in minimal kit before, after a wee
Towel off and weigh in the same kit after
Note everything you drank
Ride at your normal effort for an hour or more

The two limits

Not too little, not too much

Limit	Why
Lose under 2% of body weight	bigger losses can hurt performance in the heat
Never finish heavier	overdrinking can lead to hyponatraemia
Drink to thirst	a good guide for most rides

A fuller sweat test

Wee and a drinking schedule

The ACSM method for sweat rate is weight lost plus fluid drunk, minus any urine passed, over the time. If you stopped for a wee on the test ride, add a rough amount (a typical wee is 200 to 300 ml) and the sweat figure becomes more accurate.

Pick how often you like to drink and the page splits the next ride's range into sips. Little and often is easier on the stomach than big gulps, and it keeps you nearer the aim of losing less than 2% without finishing heavier.

Read with care

What this cannot tell you

WeatherSweat rate rises a lot in the heat.
SaltHeavy sweaters may need electrolytes on long rides.
Toilet stopsA wee during the test throws the numbers.

Questions

Common questions

How do I work out my sweat rate?

Weight lost plus fluid drunk, divided by the hours you rode.

How much should I drink per hour cycling?

Enough to lose less than 2% of your weight, and never more than you sweat.

Can you drink too much water when cycling?

Yes. Drinking far more than you sweat can dilute blood sodium, which is dangerous.

Sources

Last checked 21 October 2026. Spotted something wrong? Tell us and we will fix it.

Before you push on

New to exercise, or got a heart, lung or joint condition? Have a word with your GP or practice nurse first. Stop and get help if you feel chest pain, faintness or unusual breathlessness, and call 999 if it is severe.