Score any ride for Training Stress and Intensity Factor from your FTP, your Normalized Power and how long you rode.
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Enter your actual Normalized Power if you know it (from your head unit or training platform). Average power is only a valid stand-in for a steady effort. On a variable ride, average power will understate your real TSS. Don't have an FTP yet? Use the FTP Calculator first.
Training Stress Score boils a ride down to one figure that combines how hard you went relative to your threshold with how long you kept going. The calculator uses the published Coggan/TrainingPeaks model:
One hour exactly at FTP scores 100. Every other ride is scaled against it, which is why a three-hour spin and a forty-minute interval session can be added up on the same scale.
IF tells you what kind of ride it was. These bands are commonly cited from Allen and Coggan's work:
| Intensity Factor | Typical ride |
|---|---|
| Below 0.75 | Recovery rides |
| 0.75 to 0.85 | Endurance-paced rides |
| 0.85 to 0.95 | Tempo, sweet spot and steady group rides |
| 0.95 to 1.05 | Threshold work; a time trial of about an hour |
| 1.05 to 1.15 | Very hard intervals; short time trials (under about 30 minutes) |
| Above 1.15 | Prologues and other very short, very hard efforts |
For a rider with a 250 W FTP, here is what typical rides score:
| Ride | Duration | NP | IF | TSS |
|---|---|---|---|---|
| Easy recovery spin | 1 h | 138 W | 0.55 | 30 |
| 2-hour endurance ride | 2 h | 170 W | 0.68 | 92 |
| 3-hour endurance ride | 3 h | 175 W | 0.7 | 147 |
| 1-hour tempo ride | 1 h | 213 W | 0.85 | 72 |
| Two 20-minute threshold intervals in 75 minutes | 1.25 h | 220 W | 0.88 | 97 |
| 1-hour hard race effort | 1 h | 238 W | 0.95 | 90 |
| 1-hour ride exactly at FTP | 1 h | 250 W | 1 | 100 |
| 5-hour gran fondo | 5 h | 180 W | 0.72 | 259 |
The long, easy rides quietly out-score the short hard one: duration counts, and many riders underestimate the load of a big endurance day.
Allen and Coggan's Training and Racing with a Power Meter gives a commonly cited rough guide to how much recovery a day's TSS tends to demand. Treat it as orientation, since real recovery depends on the individual and their training history:
Beyond single rides, training platforms add daily TSS into longer-term fitness and fatigue trends. TSS is most useful at that scale, but it needs a platform that logs every ride.
True Normalized Power is computed from a full power recording: a 30-second rolling average, raised to the fourth power, averaged, then the fourth root taken. It weights hard surges more than steady riding at the same average. A single-number calculator cannot derive that, so you enter NP from your head unit or training platform. If you only have average power, use it for steady, flat efforts; on a variable ride it will understate your true TSS.
A TSS is only as accurate as the FTP beneath it. If you have not tested, the FTP calculator gives you an estimate, and the power zones calculator tells you how hard to ride during the workout itself, while TSS measures what the workout cost afterward. To plan the load before you ride, work out the watts a route will take in the cycling power calculator, then estimate the resulting IF against your FTP.
The calculator implements the published Coggan/TrainingPeaks TSS model without modification, from Allen, H. & Coggan, A. (2010), Training and Racing with a Power Meter (2nd ed.), VeloPress, and Coggan, A.R., "Normalized Power, Intensity Factor and Training Stress Score," TrainingPeaks. No coefficients are invented here. The one modeling choice is that Normalized Power is an input rather than something computed, because a power file is needed to derive it. The ride table above uses assumed NP values to show typical scores; it is not a measurement.
