Critical Power Calculator
Determine your CP and W' from time trial efforts - unlock your power-duration profile
Critical Power (CP) is the highest power output you can sustain aerobically without progressive fatigue. W' (W prime) is your finite anaerobic energy reserve above CP - think of it as your battery. Together, CP and W' define your entire power-duration relationship. Enter 2 to 5 maximal efforts of different durations and we'll calculate your power profile using the Monod and Scherrer (1965) model.
This calculator provides estimates based on the 2-parameter Critical Power model. Results depend on effort quality - all trials must be true maximal efforts. CP is not a single-session measurement: validate with field testing. Consult a coach or sports scientist for personalized training advice. TrainingZones.io is for informational purposes only.
Power Levels - Where Do You Stand?
Critical Power classification based on W/kg. Same scale as FTP but CP is typically 3-5% higher than FTP.
| Level | W/kg | Example |
|---|---|---|
🚶Untrained | 0-1.5 | 0-105W |
🚲Beginner | 1.5-2.5 | 105-175W |
🟢Recreational | 2.5-3.2 | 175-224W |
🔵Sportive | 3.2-3.7 | 224-259W |
🟣Racer | 3.7-4.2 | 259-294W |
🥉Serious | 4.2-4.6 | 294-322W |
🥈Elite | 4.6-5.1 | 322-357W |
🥇Domestic Pro | 5.1-5.6 | 357-392W |
🏆Continental | 5.6-6.2 | 392-434W |
👽World Tour | >6.2 | 434-434+W |
Testing Protocols
Two proven methods to determine your Critical Power and W'
The Science Behind Critical Power
The CP model was first described by Monod and Scherrer in 1965 and remains one of the most validated models in exercise physiology.
Hyperbolic Model - Power vs Time
Power output P for a given duration t follows a hyperbola. As time increases, power approaches CP asymptotically. The curve is fully defined by just two parameters: CP (the asymptote) and W' (the curvature constant).
Linear Model - Work vs Time
Total mechanical work W = P × t increases linearly with time. The slope of this line is CP (watts), and the y-intercept is W' (joules). This is how we calculate CP from your time trial data using linear regression.
Time to Exhaustion - The Countdown
Rearranging the formula gives the predicted time until exhaustion at any power above CP. Your W' empties at a rate of (P - CP) watts, so higher power means shorter time. Below CP, the model predicts infinite endurance (in theory).
Key Variables
Critical Power - the boundary between sustainable and unsustainable exercise intensities, in watts
W prime - your anaerobic work capacity above CP, measured in joules (J) or kilojoules (kJ)
Time to exhaustion - how long you can hold a given power above CP before W' is fully depleted
Total mechanical work - power × time, measured in joules. Represents the total energy output of an effort.