Swim pace and CSS calculator
CSS from a 400 and 200 test in metres or yards, your pace, and finish time.
Your pace will appear here.
How to get your numbers
CSS test
Swim 400-600 m easy with drills and a few short builds. Time a 400 m at your best even pace, then have 5 minutes easy or resting. Time a 200 m as hard as you can hold it, then swim down.
Getting good times
Start both efforts the same way, from a push-off, and swim them in the same session. A friend on the poolside with a stopwatch helps. Your CSS is half the difference between the two times. In a yards pool, swim 400 yd and 200 yd and choose Imperial.
Got your numbers? Put them on your Garmin, Wahoo or COROS
Only do hard tests when you're fit and well. If you have a heart condition or any doubts, check with your doctor first.
How this is worked out
Your CSS
CSS per 100 = (400 time - 200 time) / 2. With a 400 in 6:40 and a 200 in 3:10, that is (6:40 - 3:10) / 2 = 1:45 per 100.
Your finish time
Finish time = pace per 100 x distance / 100.
Metres and yards
A test in a yards pool uses the same sum and gives a pace per 100 yd. To convert, 100 yd is 91.44 m.