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Calculate swimming pace per 100m or 100yd from split times and distance. Convert between pace formats for pool and open water training plans.
Calculate even swimming split times for race pacing and interval training. Generate negative, even, or positive split targets for any distance.
Calculate pool laps, lengths, and distance from swim count. Convert between 25m, 25yd, and 50m pools for accurate distance tracking.
Subtract 200m distance from 400m and divide by the time difference between trials. This yields speed in meters per second at the aerobic-anaerobic transition.
CSS (m/s) = (400m − 200m) ÷ (T400 − T200)Convert CSS speed to seconds per 100 meters for workout planning. Most training sets use CSS + 0 to +8 seconds per 100.
CSS pace/100m = 100 ÷ CSS (m/s)Structure interval workouts around CSS pace. Threshold sets at CSS improve lactate clearance; slightly faster sets develop VO2 max.
Aerobic: CSS + 3–8s | Threshold: CSS to CSS + 3s | VO2: CSS − 3 to −8sUpdated: July 2026
400m in 6:00 and 200m in 2:50 yields CSS of 1:25/100m. Base aerobic sets at 1:30–1:33/100m for Ironman swim preparation.
Retest every 4–6 weeks. CSS improving from 1:40 to 1:35/100m confirms training adaptation and triggers interval pace updates.
750m sprint race swum at CSS + 2s per 100 (slightly conservative) balances speed with energy conservation for the bike segment.
Critical Swim Speed (CSS) approximates the fastest pace you can sustain aerobically — equivalent to lactate threshold in running. Enter your 400m and 200m time trial results to calculate CSS pace per 100m for setting training intervals and race pacing.