Amount of liquids per time per temperature?

For a long endurance ride, I am trying to calculate how much liquid I should carry. In winter (below 10 degrees celsius), I read across various sites that you should drink about 550ml of liquids per hour when you are about my weight (73kg).

Is anybody aware of a table where you can look up liquids per temperature and body weight?

It influences the number of stops I need to make, and the size of the bidons I will carry (and thus the weight of my bike and total time).

Conditions can vary on the day. Carry large bidons, plan on a lot of stops. If you have only gone through 3/4 of your 1st bidon at a planned stop, continue on until the next planned stop.

The difference in weight between a large (800ml) versus a regular (550 ml) is 2 x 250g = 500g. If you save just one stop through carrying extra water, you will more than save the time 0.5kg would cost you. Plus you have a contingency if conditions are warmer/slower than expected.

It also depends on how warm you are, ie how hard you’re working, how many clothes you wear, and how much water you lose (sweat, breathing). So it’s hard to give a simple equation to use.

Also depends hugely on intensity. I’ve done winter (0-5C) endurance rides where I’ve drunk half a bidon in 3 hours and even that is enough that I still need a couple of pee stops. And I’ve done hot summer rides (25-35C) with a lot of intensity where I’ve drunk 2 large bidons an hour (so ~4.5 litres in 3 hours) and still been pretty dehydrated afterwards.

From The RP Diet for Endurance: (the book I wrote and profit from)

Sweat Rates @ ~85 degrees during running.
There are tables for lower temps in the book too.

Electrolyte Content of Sweat

Not many useful studies on sweat rates during cycling so I didn’t attempt to form tables for that in the book.

Note: sweat rate and electrolyte content of sweat are affected by:

  1. Genetics
  2. Fitness
  3. Heat acclimatization
  4. Wind
  5. Clothing
  6. Intensity of exercise

Makes it VERY hard to predict especially broadly for a population.

Weighing yourself pre- and post-training is by far and away the best way to gauge sweat rate. Hold your urine if possible. Weigh naked and dry both pre- and post-training.

Real talk…I’m a PhD in Sport Physiology, obsessed with performance, have a highly competitive cyclist/triathlete wife for whom I manage all training/racing/nutrition… we don’t weigh pre- & post-training. We don’t sweat test.

We do this:

  1. When not sweating noticeably, and it’s not anticipated that sweat production will be substantial: drink to thirst. Use 300-800mg sodium per liter.
  2. When sweating noticeably, we just assume that sweat rates will outpace maximum replacement rates. Therefore, we seek to max out fluid and sodium consumption as tolerated by gut. ~1-1.2L per hour, and 1000-1800mg sodium per liter.

Drink to thirst after training, and include at least half as much sodium per liter as you did during training.

With experience doing the above, you’ll start to learn how much you ought to carry.


These guys hold some of the answers you’re looking for. They (Andy Blow) also featured in one of TR’s podcasts.