Free Running TSS Calculator
Calculate Training Stress Score for running workouts - The only free sTSS calculator
What is Running TSS (sTSS)?
Running Training Stress Score (sTSS) quantifies the training load of a running workout by combining intensity and duration. It's adapted from cycling's TSS methodology, using your Critical Run Speed (CRS) as the threshold pace. A 1-hour workout at CRS pace = 100 sTSS.
Free sTSS Calculator
Calculate training stress for any running workout. Requires your CRS pace.
How sTSS is Calculated
Formula
Where:
- Intensity Factor (IF) = CRS Pace / Average Workout Pace
- Duration = Total workout time in hours
- CRS Pace = Your threshold pace from CRS test
Worked Example
Workout Details:
- CRS Pace: 1:49/100m (109 seconds)
- Workout Duration: 60 minutes (1 hour)
- Average Pace: 2:05/100m (125 seconds)
Step 1: Calculate Intensity Factor
IF = 109 / 125
IF = 0.872
Step 2: Calculate sTSS
sTSS = 1.0 × 0.760 × 100
sTSS = 76
Interpretation: This 60-minute workout at easy pace (slower than CRS) generated 76 sTSS - a moderate training load suitable for aerobic base building.
Understanding sTSS Values
| sTSS Range | Training Load | Recovery Time | Example Workout |
|---|---|---|---|
| < 50 | Low | Same day | Easy 30-min run, technique drills |
| 50-100 | Moderate | 1 day | 60-min endurance, steady pace |
| 100-200 | High | 1-2 days | 90-min threshold sets, race pace intervals |
| 200-300 | Very High | 2-3 days | 2-hour hard training, multiple threshold blocks |
| > 300 | Extreme | 3+ days | Long race (>2 hours), ultra-endurance |
Weekly sTSS Guidelines
Target weekly sTSS depends on your training level and goals:
Recreational Runners
Weekly sTSS: 150-300
2-3 workouts per week, 50-100 sTSS each. Focus on technique and building aerobic base.
Fitness Runners / Triathletes
Weekly sTSS: 300-500
3-4 workouts per week, 75-125 sTSS each. Mix of aerobic endurance and threshold work.
Competitive Masters Runners
Weekly sTSS: 500-800
4-6 workouts per week, 80-150 sTSS each. Structured training with periodization.
Elite / Collegiate Runners
Weekly sTSS: 800-1200+
8-12 workouts per week, double days. High volume with recovery management critical.
⚠️ Important Notes
- Requires accurate CRS: Your CRS must be current (tested within 6-8 weeks) for accurate sTSS.
- Simplified calculation: This calculator uses average pace. Advanced sTSS uses Normalized Graded Pace (NGP) which accounts for interval structure.
- Not for technique work: sTSS only measures physical training stress, not skill development.
- Individual variation: Same sTSS feels different for different runners. Adjust guidelines based on your recovery.
Why sTSS Matters
Training Stress Score is the foundation for:
- CTL (Chronic Training Load): Your fitness level - 42-day exponentially weighted average of daily sTSS
- ATL (Acute Training Load): Your fatigue - 7-day exponentially weighted average of daily sTSS
- TSB (Training Stress Balance): Your form - TSB = CTL - ATL (positive = fresh, negative = fatigued)
- Periodization: Plan training phases (base, build, peak, taper) using target CTL progressions
- Recovery Management: Know when to push and when to rest based on TSB
Pro Tip: Track Your CTL
Record daily sTSS in a spreadsheet or training log. Calculate your 42-day average (CTL) weekly. Target 5-10 CTL points increase per week during base building. Maintain or slightly reduce CTL during taper (1-2 weeks before race).
Frequently Asked Questions
What is Running TSS (sTSS)?
Running Training Stress Score (sTSS) is a metric that quantifies the training load of a running workout by combining both intensity and duration. It's adapted from cycling's TSS methodology, using your Critical Run Speed (CRS) as the threshold pace. A workout of 1 hour at CRS pace equals 100 sTSS.
How do I calculate my sTSS?
Use the calculator above by entering your CRS pace (from a CRS test), total workout duration, and average pace during the workout. The formula is: sTSS = Duration (hours) × Intensity Factor² × 100, where Intensity Factor = CRS Pace / Average Workout Pace.
Do I need CRS to calculate sTSS?
Yes, your Critical Run Speed (CRS) is required to calculate the Intensity Factor, which is essential for sTSS calculation. CRS represents your threshold pace and should be tested every 6-8 weeks. You can find your CRS using our CRS calculator.
What's a good sTSS score for one workout?
It depends on workout intensity: Easy workouts typically score below 50 sTSS, moderate workouts 50-100 sTSS, hard workouts 100-200 sTSS, and very hard workouts above 200 sTSS. The appropriate score depends on your training goals and current fitness level.
How much sTSS should I do per week?
Weekly sTSS targets vary by level: Recreational runners: 150-300, Fitness runners/Triathletes: 300-500, Competitive Masters: 500-800, Elite/Collegiate: 800-1200+. Start conservatively and increase gradually to avoid overtraining.
Is running TSS the same as cycling TSS?
The concept and formula are the same, but sTSS is adapted for running. Instead of using power (FTP) like cycling TSS, sTSS uses pace with CRS as the threshold. Both measure training load using Duration × Intensity Factor² × 100.
Can I use sTSS for all run strides?
Yes, but your CRS should be stride-specific. Most runners use freestyle CRS since it's the most commonly trained stride. If you train primarily in another stride, perform a CRS test in that stride and use that pace for sTSS calculation.
What's the difference between sTSS and CTL/ATL/TSB?
sTSS measures a single workout's training load. CTL (Chronic Training Load) is your long-term fitness, ATL (Acute Training Load) is your recent fatigue, and TSB (Training Stress Balance) is your freshness. These metrics use sTSS values over time to track your training state. Learn more in our Training Load guide.
Related Resources
CRS Test
Need your CRS pace? Use our free CRS calculator with 5K and 3K test times.
CRS Calculator →Training Load Guide
Learn about CTL, ATL, TSB and Performance Management Chart metrics.
Training Load →Run Analytics App
Automatic sTSS calculation for all workouts. Track CTL/ATL/TSB trends over time.
Learn More →Want automatic sTSS tracking?
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