Training Stress Score (TSS) Calculator
Quantify a session from power, FTP, and duration.
What TSS measures
Training Stress Score (TSS) puts a single number on how much a ride takes out of you, combining intensity and duration. By definition, one hour ridden right at your FTP scores 100. A long, easy ride and a short, brutal one can land on the same TSS — which is exactly the point: it lets you compare and plan very different sessions on one scale.
The formula
First, Intensity Factor (IF) = Normalized Power ÷ FTP — how hard the ride was relative to threshold. Then TSS = (seconds × NP × IF) ÷ (FTP × 3600) × 100. Using true Normalized Power rather than a flat average gives a more honest score for variable, surgy rides.
Reading the load
As a rough daily guide: under 150 is a low-stress day, 150–300 is moderate, 300–450 is a high-load day, and over 450 is very high — the kind of effort that usually needs real recovery before the next hard session.
Questions
What is TSS?
Training Stress Score combines how hard and how long a session was into one number. By definition, one hour at exactly your FTP equals 100 TSS, so it scales intensity and duration together.
How is it calculated?
IF = normalized power ÷ FTP, and TSS = (duration in seconds × NP × IF) ÷ (FTP × 3600) × 100. Enter normalized power if you have it; average power is a rough substitute for steady efforts.
What do the numbers mean?
Roughly: under 150 TSS is low and recovers fast, 150–300 is moderate, 300–450 is high, and above 450 is very demanding. They are most useful tracked over weeks as training load.