Training load calculator
rTSS calculator
Enter your pace and duration below to calculate the running training stress score (rTSS) for this run.
rTSS (running Training Stress Score) measures how hard a run was relative to your threshold pace, on the same scale as power-based TSS: 100 equals one hour at threshold.
- Intensity Factor (IF) = threshold pace / average pace
- rTSS = duration in hours × IF² × 100
A 45-minute run at 5:00/km with a threshold pace of 4:30/km gives an IF of 0.90 and an rTSS of 61.
It's the fastest pace you could hold for 45 to 60 minutes. If you run 10K in over 45 minutes, your 10K race pace is a good estimate. If you're faster than that, use your half marathon pace instead. A hard training run of 45 to 70 minutes works too: take the average pace.
Pace, in most cases. Heart rate takes a few minutes to catch up with the effort, so a short run comes out lower than it deserves. Pace responds immediately, and it works on runs you recorded without a heart rate strap. Heart rate still earns its place on long runs in heat, where pace drops for reasons the pace model can't see.
This calculator uses your average pace, so a hilly run comes out lower than it felt. Running uphill at a given pace costs more than running flat at the same pace. Some platforms adjust for this with a graded pace, which raises the score on climbs and lowers it on descents.
rTSS uses the same scale as TSS and HRSS, so the same ranges apply:
- Under 50 - easy, you'll recover quickly
- 50 to 100 - solid session, normal training day
- 100 to 150 - hard day, you'll feel it tomorrow
- 150 to 300 - long run or race effort, plan recovery
- Over 300 - marathon or ultra territory
One run's score is useful, the trend is what matters. Shape Calendar calculates rTSS for every run you sync from Garmin, Wahoo or Apple Health, and combines it with power-based TSS from your rides on one chart, so your whole week is in one place.
Shape Calendar
Plan runs by load, not by guesswork.
Type “5×1km at threshold” and Shape builds the workout, predicts its load, and syncs it to your Garmin, Apple Watch or Wahoo.