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 & 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 & 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.