CSS or Critical Swim Speed is simply an estimate of what pace you can hold for around 20 minutes of swimming. It’s a pace we should be hitting a lot in training and also a great measure of your improvements. Its very similar to using threshold in running or FTP in cycling.

You can check out how to do a CSS Test HERE

Then plug your results into our calculator HERE

When it comes to training to your CSS pace you have a few options! We’ll talk about both…

  1. Using a Tempo Trainer (our preferred method!)

Using a Tempo Trainer you can key on your pace per length using Mode 1. You then simply hit the single reset button at the start of each rep and it’ll beep when you should be at the end of each length!

The benefit of this is that not only will you hit your CSS pace for the rep, you’ll also (hopefully) pace the lengths within the rep evenly as you have some feedback along the way.

Example: You are aiming for 2:00 per 100m so you put the tempo Trainer on 30:00 mode 1 (for 25m pool) and get to hear the beep at the end of each length!

You can buy a Tempo Trainer HERE

  1. Using a pool clock (Old school method!)

You can of course simply swim your rep and then check the time/pace on your watch or the pool clock. So, if you are aiming for 2:00 per 100m you can figure your targets from that (4:00 for 200m etc). The downside to this method is you get no feedback within the rep – so you could be hitting 2:00 per 100m, but not necessarily as a nice even 30 seconds per length!

Example: You are aiming for 2:00 per 100m so you simply look at the clock or your watch at the end of the rep and hope you’ve swam it at the correct speed!

Variants of CSS Pace…

We don’t need to always swim to exactly CSS Pace. In some cases, you might swim at a slower pace, for example:

‘CSS Pace + 4 seconds per 100m’

In the example above, if your CSS was 2:00, you simply add 4 seconds to get 2:04 per 100m, then divide it by your pool length…! So, you’d be on 31:00 per length for a 25m pool.


Of course, you don’t need to use CSS Pace for every session, its great to simply use easy/medium/fast for some sessions, but hopefully this guide helps you figure out the best way for you to train to your CSS pace 😊