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Swim CSS Calculator – Find Your Pace, Training Zones & Race Time

Quickly calculate your critical swim speed (CSS), set custom training zones, and predict your race finish times. Enter two swim results below for instant feedback you can use in every workout.

Understanding Your Swim Data

Swim Speed (CSS) Training Zones Calculator
Swim Speed (CSS) Calculator

Calculate your Critical Swim Speed and personalized training zones for optimal swim performance.

Shorter Distance Test
Longer Distance Test
How This Calculator Works

Critical Swim Speed (CSS) represents your lactate threshold pace:

  • Test with two time trials at different distances
  • CSS approximates the pace you can maintain for 30-60 minutes
  • Training zones are based on percentages of your CSS
  • Ironman predictions use zone-appropriate pacing for each distance

Need help?

Swim CSS Calculator: FAQs

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