Swimming Calculators
Critical Swim Speed from a 400m and 200m time trial, or T-Pace from a 1000m test, with training zones.
Swim a maximal 400m and a maximal 200m on the same day with 10–15 min rest between.
M:SS
M:SS
Swim a maximal 1000m time trial. T-Pace = total time / 10.
M:SS or H:MM:SS
Methodology
CSS Calculator derives your Critical Swim Speed from a 400m and 200m time trial on the same day.
T-Pace Calculator uses a single 1000m effort to set your threshold pace.
Critical Swim Speed
CSS is the swimming equivalent of lactate threshold, roughly the fastest pace you can hold for 1500m without blowing up. It gives you a personal anchor for all training zones.
CSS = (T400 - T200) / 2 (seconds per 100m)
The logic: your 400m and 200m both tax your aerobic system. The difference between them, divided by two, isolates the aerobic contribution per 100m.
Source: Swim Smooth (Newsome & Young). Widely used in triathlon and open-water coaching.
T-Pace
T-Pace comes from a maximal 1000m time trial:
T-Pace = T1000 / 10 (seconds per 100m)
Simpler to test than the CSS protocol, and close enough to CSS for most training purposes. A good starting point if you haven’t done the two-distance CSS protocol.
Zone Models
Zones are expressed as pace offsets from your threshold (CSS or T-Pace). Positive offset = slower. Negative = faster.
| Model | Zones | Suited to |
|---|---|---|
| CSS 5-Zone | 5 | Triathlon, open-water, general fitness swimming |
| T-Pace 5-Zone | 5 | Pool training, simpler test protocol |
| EN/SP Competitive | 6 | Competitive pool swimmers, club training |
Note: Results are estimates based on population averages. Individual responses vary. Nothing here is medical advice. Talk to a doctor or coach before changing your training or nutrition.