Ftp Power Zone
Calculator

FTP, or Functional Threshold Power, is the highest power output you can sustain for approximately one hour, and training zones are calculated as percentage ranges of that number, such as 56-75% for endurance or 105-120% for VO2max work. Once you know your FTP, the calculator generates all zone boundaries automatically.

The gold-standard test is a 60-minute maximal time trial, but a common shortcut is a 20-minute maximal effort with the result multiplied by roughly 0.95, since a 20-minute max effort is unsustainable for the fully hour that would fatigue power slightly more. Ramp tests and other protocols also exist, each with slightly different assumptions.

Power output responds instantly to effort, while heart rate lags behind and drifts upward over a long ride even at constant power due to heat and dehydration, making power a more precise and immediate intensity indicator. This is why serious cyclists with power meters typically train primarily by power zones rather than heart rate.

Every 6-8 weeks is a common interval, or after a significant training block or detraining period, since FTP changes as fitness improves or declines and outdated zones misrepresent your current training intensities. Testing too frequently can also interfere with training consistency.

Perceived effort at a fixed power output is influenced by fatigue, sleep, nutrition, heat, and hydration status, so a workout at 90% FTP can feel notably harder on a poorly recovered day even though the power number itself hasn't changed. Power zones measure objective output, not subjective difficulty on any given day.