Critical Swim Speed Training Zone Calculator​


Use this simple calculator to calculate your Critical Swim Speed (CSS) and estimate your ideal swim speed training zones in meters or yards. 

A Critical Swim Speed test is a simple way to measure your swim fitness. It estimates the pace per 100 that you would maintain during a maximal 1500 meter or yard time trial. 

To test your CSS pace, you would swim a maximal 400 and 200 time trial within the same session, with a five-minute active recovery between, and time yourself for both. Then simply enter your times below and let the calculator do its magic! 

To learn more about CSS, you can read our introduction to CSS training underneath the calculator below.

After calculating your swimming pace zones, you can also print your results or download as a PDF below. Enjoy!

Critical Swim Speed Training Zone Calculator

How should I calculate my values? Swim a maximal 400 and 200 time trial within the same session, with a five-minute active recovery between, and time yourself for both. Enter your 400 and 200 times below.

Step 1. Calculate My Critical Swim Speed (CSS)

Step 2. Calculate My Swim Speed Training Zones

Swim Speed Training Zones Feel Swim Speed (mm:ss / 100 meters or yards)
1 Easy
2 Steady
3 Moderately Hard
4 Hard
5 Very Hard

About CSS Training

CSS stands for Critical Swim Speed – a really simple concept that could improve your swim fitness, pace judgement and training motivation.

Here we’ll explain what CSS is, how it can make you fitter and how to test your CSS (using our own CSS Calculator found on this page). We’ll also give you some sample CSS training sessions.

What Is CSS?

CSS is the pace at which you’d currently swim a 1500 Time Trial (in yards or metres). It’s nothing complicated. Simply a useful fitness yardstick for endurance swimming events of 400 and above. Here’s why:

The Benefits of CSS Training

  1. CSS is a pace that’s tough enough to develop your aerobic capacity but not so hard that it’ll take you days to recover. So you can improve your swim fitness and still have enough energy to go running or cycling (or swimming again?!)
  2. CSS is a race-specific training pace. It may not make you the fastest 50 or 100 swimmer, but it will train you to sustain a moderately high speed for longer distances.
  3. CSS training teaches you about pace awareness the hard way (which is usually the best way!) Go off too fast and you’ll pay the price later. Ouch!
  4. Thankfully you can test your current CSS pace without having to swim a solo 1500 Time Trial. See below for instructions.
  5. Once you know your CSS pace, you can use a Finis Tempo Trainer Pro to help you train. It’s a small beeping device that attaches to your goggles. Dial in your CSS pace and it’ll happily beep every lap so that you can maintain perfect pace.

How To Test Your CSS

To test your current CSS pace you need to swim a 400 and 200 Time Trial within the same session. Ideally, get a friend or coach to time you and record your 100 splits and strokes per minute. Failing that, simply record the 400 and 200 times yourself. Once you’re done, enter your 400 and 200 times into our own CSS Training Zone Calculator.

CSS Sample Workouts

Once you’ve worked out your CSS pace, the training possibilities are endless. You could start off by trying these four simple workouts. You can shorten them if you’re not quite ready for 2000 metres or yards yet. Don’t forget to include a warm up (400-800m/y) and warm down (100-200m/y) too.

1.       20 x 100 with 15 secs recoveries. All at CSS

2.       10 x 200 with 20 secs recoveries. All at CSS

3.       5 x 400 with 30 secs recoveries. All at CSS

4.       3 x 600 with 45 secs recoveries. All at CSS

We have also recently put together our top 7 swim workouts for triathlons, which you can download as a PDF for free and print off to use for your next sessions. 

Conclusion: CSS Training

Including CSS sets into your swim training can help improve your sustainable speed and enhance your pace judgement. In addition to CSS training, it’s also important to strike a balance between speed, threshold and endurance workouts in order to meet the needs of your target races. Technique work and open water training are equally important too!
Share on facebook
Share on linkedin
Share on twitter
Share on print
Phil Mosley (Coach & Founder)
Phil Mosley (Coach & Founder)

Phil is a recognised expert in the field, having featured on many endurance sports publications. He founded MyProCoach in 2010 to sell premium training plans complete with email coach support for triathlons, duathlons, running & cycling.

Popular Articles

About Phil Mosley

About Phil Mosley

Phil is a successful coach & athlete, having sold over 10,000 training plans on TrainingPeaks and been featured on countless publications. His focus is on smart training that still leaves quality time for your family, friends & career. You can browse learn more about MyProCoach here or preview your training plan now.

Trial us with our FREE taster training plans!

*Plus, you’ll also receive free regular training advice from head coach Phil Mosley! Unsubscribe at any time.

Big news...

We've made some of our plans 100% FREE!

Choose your event:
5.0/5 from 320+ reviews ⭐⭐⭐⭐⭐

*Plus, you’ll also receive free training advice via email from head coach Phil Mosley! Unsubscribe at any time.

We're Sorry To See You Go!

Please confirm your cancellation below and one of our team will process it as soon as possible (stopping all future payments). Your subscription will still continue until the end of your current billing cycle (your “next payment date”) and there is nothing else you need to do.

Don’t worry, you will always be able to access your completed workouts and your TrainingPeaks login credentials will stay the same. Also, if any payments happen to come out before we cancel your subscription, we’ll simply refund them.