Critical Swim Speed

CSS calculator.

Swim a 400 and a 200 time trial fresh. We derive your Critical Swim Speed — the pace you can hold for ~30 minutes — and a full set of training zones.

400m time (m:ss)

200m time (m:ss)

Pool length

CSS pace (per 100m)

1:35.0

Z1 · Easy / Recovery

1:52.1/100m·0:28.0/25m

Z2 · Aerobic

1:44.5/100m·0:26.1/25m

Z3 · Tempo

1:38.8/100m·0:24.7/25m

CSS · Threshold

1:35.0/100m·0:23.8/25m

Z5 · VO2 / Race

1:31.2/100m·0:22.8/25m

Z6 · Speed

1:27.4/100m·0:21.9/25m