Critical Swim Speed Calculator CSS

CSS Pace Calculator
3
Unit
Enter your time:
1
Time for 400m
minutes
seconds

1
Time for 200m
minutes
seconds

calculate
CSS Pace:
-
Actual speed:
-


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What is Critical Swim Speed (CSS)?

Critical Swim Speed (CSS) is the pace you can maintain over a long distance without exhaustion. Often called your โ€œthreshold pace,โ€ CSS is a key metric for endurance training and is widely used by coaches to set training zones and track aerobic fitness improvements in swimmers.

How to Use the CSS Calculator

  1. Swim a 400m (or 400y) time trial and record your time.
  2. Rest fully, then swim a 200m (or 200y) time trial and record your time.
  3. Enter both times into the calculator and select meters or yards.
  4. Click Calculate to find your CSS pace per 100m or 100y.

Note: Use your personal bests or recent time trial results for the most accurate calculation.

How is CSS Calculated?

CSS is calculated using the formula:
CSS (m/s) = (Distance1 - Distance2) / (Time1 - Time2)
Where Distance1 and Distance2 are typically 400m and 200m (or yards), and Time1 and Time2 are the respective times in seconds.

Why Use CSS in Training?

  • Set precise training zones for endurance and threshold workouts.
  • Track aerobic fitness improvements over time.
  • Develop personalized training plans and interval sets.

Interpreting Your CSS Results

  • CSS Pace: Your sustainable pace per 100m or 100y for long-distance swimming.
  • Training Zones:
    • Recovery: CSS + 15โ€“20 seconds per 100
    • Aerobic Base: CSS + 10โ€“15 seconds per 100
    • Threshold: CSS ยฑ 2โ€“3 seconds per 100
    • VO2 Max: CSS โ€“ 5โ€“10 seconds per 100
  • Sample Workout: 10 ร— 100m at CSS pace with 10โ€“15 seconds rest.

Frequently Asked Questions

Q: How often should I test my CSS?
A: Every 4โ€“6 weeks or after a training block to monitor progress.

Q: What if my 400m and 200m times are very close?
A: This may indicate pacing issues or fatigue; retest when well rested for best results.

Q: Can I use CSS for open water training?
A: Yes, CSS is an excellent benchmark for open water endurance training and pacing.

Related Swim Calculators

  1. Swim Pace Calculator
  2. Goal Time Calculator
  3. Yards Goal Calculator
  4. Race Review Calculator
  5. Medley Relay Calculator

Note: Critical Swim Speed (CSS) Calculator Update June 2025

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