Enter your recent 400m and 200m time trial results. The CSS protocol remains metric; results can also be displayed per 100 yards.
| Distance | Target Time |
|---|---|
| 100m | 01:35 |
| 200m | 03:10 |
| 400m | 06:20 |
| 1500m | 23:45 |
Estimate Critical Swim Speed (CSS) from 400 m and 200 m time trials, then inspect transparent pool-pace references. The result is a two-trial field estimate; it does not guarantee a pace you can sustain indefinitely or prescribe a complete training set.
Critical Swim Speed (CSS) uses a 400 m and 200 m time trial as a two-point distance-time model. This calculator reports the resulting pace per 100 m and the equivalent per 100 yd as a repeatable field reference, not a fatigue-free pace.
Warm up, swim each distance as a hard time trial, and allow enough recovery that the second effort is meaningful. Record moving swim time without rest. For a valid model, the 400 m time must be more than twice the 200 m time.
CSS speed is the 200 m difference in distance divided by the difference between the two finishing times. The calculator converts that speed into pace per 100 m, per 100 yd, and longer split projections.
Because both trials contribute, an inaccurate 200 m or 400 m effort can noticeably move the result. Repeat the pair under similar pool and rest conditions when tracking fitness.
CSS is a useful reference for sustained aerobic and threshold-oriented sets. Short repetitions may be faster, while longer continuous work may need to be slower. Use repeat quality, rest interval, stroke integrity, and perceived effort alongside the pace.
CSS speed equals (400 m minus 200 m) divided by the difference between the 400 m and 200 m times. Pace is the reciprocal of that speed, scaled to 100 m or 100 yd.
This implementation expects 400 m and 200 m test results. It converts the resulting pace to yards for training display, but it does not relabel 400 yd and 200 yd trials as meters.
The cited method study does not establish a universal retest interval. As a practical coaching heuristic, retest after a meaningful training block or when the result is unlikely to disrupt training. Keep the pool length, warm-up, recovery, and timing method consistent so the trend is interpretable.