What exactly does TSS mean?

TSS stands for Training Stress Score and quantifies the load of a training session. One hour at threshold equals 100 TSS.

Can I calculate TSS without a power meter?

Yes. Running needs only your pace relative to threshold pace, swimming your pace per 100 metres relative to CSS.

How much weekly TSS makes sense?

Recreational athletes typically sit between 250 and 450 TSS per week. Gradual progression matters more than the absolute number.

TSS Calculator

Training Stress Score for bike, run and swim

Duration (min)

Avg pace (min/km)

min

sec

Threshold pace (min/km)

min

sec

67 TSS

Intensity Factor (IF): 0.82

What is Training Stress Score?

Training Stress Score (TSS) measures how much a single session taxed you. It combines duration and intensity into one number, which makes 40 hard minutes comparable to two easy hours.

The yardstick is your own threshold: one hour exactly at threshold equals 100 TSS. A value of 50 therefore means roughly half the strain of a hard hour, no matter whether you ran, rode or swam.

The concept comes from Andrew Coggan and Joe Friel and underpins fitness and fatigue curves as well.

How it is calculated

TSS = duration in hours × IF² × 100. The intensity factor IF is average power / FTP on the bike, threshold pace / actual pace when running, and CSS / actual pace when swimming.

Intensity is squared because an hour at threshold taxes the body far more than two hours at half that intensity — the formula is built to show that difference.

Bike example: 90 minutes at 200 W with an FTP of 250 W. IF = 200 / 250 = 0.8. TSS = 1.5 × 0.8² × 100 = 1.5 × 0.64 × 100 = 96.

Run example: 60 minutes at 5:30 min/km with a threshold pace of 4:30. IF = 270 / 330 = 0.82. TSS = 1 × 0.82² × 100 = 67.

To calculate TSS you only need one threshold value and the session — without an FTP or threshold pace it stays a guess.

How to read the number

Intensity counts for more than duration: half an hour hard can outweigh a full easy hour.

Per week, as rough guidance: beginners 150–250, recreational 250–450, committed age groupers 450–650, advanced 650–900. These are reference points, not targets — what matters is that the number grows slowly over months rather than jumping.

Frequently asked questions

What exactly does TSS mean?: TSS stands for Training Stress Score and quantifies the load of a training session. One hour at threshold equals 100 TSS.
Can I calculate TSS without a power meter?: Yes. Running needs only your pace relative to threshold pace, swimming your pace per 100 metres relative to CSS.
How much weekly TSS makes sense?: Recreational athletes typically sit between 250 and 450 TSS per week. Gradual progression matters more than the absolute number.