W' represents the 'battery' of anaerobic energy available for efforts above threshold. Typical trained values range from 15-25 kJ. A rider with a CP of 270W and a W' of 20 kJ can sustain 320W for ~400 seconds before W' depletes. W' recharges during recovery at rates proportional to how far below CP you drop. The W' / CP framework is more accurate for predicting short-effort performance (1-20 minute range) than FTP-based zones. Intervals.icu, WKO5, and Golden Cheetah calculate CP and W' from ride data automatically.