CSS Swim Pace Calculator

Critical Swim Speed Test

Calculate your training paces.

Calculate your swimming training paces and zones

When you look at your swimming program, have you ever wondered what the best pace should be swimming for different sets, for drills, for long intervals and sprints?

As no two athletes are the same, you could benefit most from individualising the paces to your ability or current fitness.

What are your individual training zones?
The CSS swim test can help you calculate your optimal swimming paces so that you get the most out of each training session.

Table of Contents

What are the benefits of the CSS Test?

The benefits of the CSS test include:

  • Improved training: by determining a swimmer’s CSS, coaches can create more effective and personalised training programs. The test results can be used to set pace targets and monitor progress over time.
  • Increased motivation: knowing your CSS can help set realistic performance goals and track their progress. This can be a powerful motivator to keep training and pushing oneself to improve.
  • Better racing strategy: Knowing one’s CSS can help swimmers to pace themselves correctly during races, leading to better performance and faster times.

What equipment is needed for a CSS Swim Test?

  • a 25m or 50m swimming pool
  • and a stopwatch.
Additional Equipment (not essential) – Polar Verity Sense or Polar OH1 to measure Heart Rate

How to perform the CSS Swim test

The protocol for the CSS test

  • Warm-up: Start with a proper warm-up of at least 10 minutes, including easy swimming, stretching and a few short sprints to get the blood flowing.
  • Test distance: The most common distances used are 400 and 200 meters.
  • The number of rounds: Typically, the test is done once.
  • Rest intervals: The swimmer should rest for the same time between each time trial.
  • Pacing: The swimmer should try to maintain a steady pace throughout each time trial, without going out too fast or slowing down too much.
  • Recording: Times for each Time Trial should be recorded to track the swimmer’s progress.

The Critical Swim Speed test

The methodology of the CSS test involves swimming a set distance, typically 400 and 200 meters. The swimmer’s time for each TT is recorded, as well as the 100m split times.

WU: (Warm-Up)

200m Swim Easy

200m Kick Moderate with a board

200m Swim Moderate

100m Kick Moderate on Back

6x50m Swim Build (Moderate -> Strong), on 1 minute

Rest 1 min

MS: (Main Set)

400m Swim Time Trial

Rest 1 min

200m Swim Easy

Rest 1 min

200m Time Trial

LD: (Loosen Down)

200m Swim Easy

*Record Time for the 400m TT

**Record each 100m split

***Record Time for the 200m TT

****Record each 100m split

Your Training Zones

Upon completing the CSS test, submit the data requested in the form above.

You will receive your individualised training zones via email within minutes.

Z1 – Easy

Your Warm-up and Loosen-Down pace:

Use this pace for your warm-up and loosen down as well as anything denoted as “easy swimming”.

This is also your pace for doing drills and kicking sets.

Drills should always be performed slowly so that you can give 100% concentration on mastering the actions.

Z2 – Moderate

Your Aerobic Pace:

Use this pace for long intervals of 600m or longer, open water swims, paddles & pull buoy sets.

You should never feel out of breath when performing these sets. These are the swimming sets that build your stamina for CSS and T-Pace training so it is very important to control your aerobic pace very rigidly.

Z3 – Cruise

Your CSS Pace:

CSS swim sets are usually 100m, 200m, 300m, 400m or even 600m repeats.

The pace should not feel super hard at first, but you will feel fatigued towards the end of the set, so try to reign yourself in at the beginning in favour of holding an even pace all the way through the set. Examples of CSS swim workouts can be viewed on our swim blog posts

Z4 – Hard

Your T-Pace: (Threshold Pace)

T-Pace swim sets of 100m, 150m, 200m, 250m repeats

The pace will feel hard, but you will get long rest periods to recover. The T-Pace sets are usually short so “Hang Tough”.

Be aware of keeping your style as strict as possible for as long as you can. If you feel you are starting to “thrash” the water and forcing your stroke, rather slow your pace by 5 seconds per 100m

Z5 – Fast

Your Sprint Pace


In conclusion, the CSS test is an effective tool for measuring a swimmer’s endurance and performance level.


By determining a swimmer’s CSS, coaches can create more effective training programs, swimmers can set realistic performance goals and track their progress, leading to better performance and faster times.


It’s a useful tool for swimmers of all levels, from beginners to elite athletes.