What FTP and VDOT actually measure
FTP (Functional Threshold Power) is the highest power you can hold for one hour without your performance falling off a cliff. It anchors your cycling zones and lets you compare effort across rides. VDOT, from Jack Daniels' running formula, does the same job for runners: a single number that captures your current aerobic ceiling and translates into pace zones.
Picking the right test
Each FTP test has its own scaling factor:
- 20-minute test: 95% of average power. The gold standard if you can stomach the duration.
- 8-minute test: 90% of average power. Easier to execute but tends to overestimate for less-trained riders because anaerobic capacity contributes more.
- Ramp test: 75% of peak 1-minute power. Quickest but most sensitive to anaerobic fitness.
Enter your test power and body weight. The calculator returns FTP, watts per kilogram, and your Coggan category (Cat 5 under 2.5 W/kg, Cat 1 above 4.4 W/kg, Pro above 5.0). Add a recent running race result and you also get VDOT calculated from race speed sustained as a fraction of VO2max.
Confidence and when to retest
The confidence score is 60% with one test, 80% with two, 95% with three or more sources. Retest every 6 to 8 weeks during a build, or sooner if your training load shifts substantially.
FTP & VDOT Estimator
Combine your cycling test data with race results for a confidence-weighted fitness estimate. See your W/kg category and running VDOT side by side.
FAQ
Which FTP test is most accurate?
The 20-minute test (95% of average power) is the gold standard. The 8-minute test tends to overestimate for less trained athletes, and ramp tests can be affected by anaerobic capacity. We adjust each with standard scaling factors.
What do the W/kg categories mean?
They follow Coggan's classification: Cat 5 (<2.5), Cat 4 (2.5-3.2), Cat 3 (3.2-3.8), Cat 2 (3.8-4.4), Cat 1 (4.4-5.0), and Pro (>5.0 W/kg). These are based on male thresholds.
Why combine FTP and VDOT?
Many triathletes and multi-sport athletes need both metrics. Combining them in one tool with a shared confidence score gives you a holistic view of your cycling and running fitness.
Methodology
FTP is estimated using Coggan's standard scaling: 95% for 20-min, 90% for 8-min, 75% for ramp tests. VDOT uses the Jack Daniels formula relating race speed to VO2max fraction sustained. Confidence score is 60% with one data source, 80% with two, and 95% with three or more.
Want to verify the math?
Explore 170+ reference calculators built by engineer-athlete Thomas Prommer. The technical foundation behind our AI.
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