Every 6-8 weeks during training. More often is just more pain for noisy data.

Indoor FTP often reads 5-10% lower (heat, no momentum, mental fatigue). Track them separately.

Ramp test vs. 20-min?

Ramp test (Zwift) is faster but tends to over-estimate FTP for anaerobic riders. 20-min is the gold standard.

Critical Power model (3-min + 12-min tests) and TrainerRoad AI FTP detection are alternatives. All converge within ±5%.

FTP from 20-Minute Test Calculator

Functional Threshold Power = 20-min average power × 0.95. The standard cycling test protocol.

Result

FTP estimate

266 W

280 W × 0.95 = 266 W.

20-min average280 W
Scaling factor0.95
FTP266 W
Z1 Active recovery≤ 146 W (≤ 55% FTP)
Z2 Endurance147-200 W (56-75%)
Z3 Tempo201-239 W (76-90%)
Z4 Threshold240-279 W (91-105%)
Z5 VO2 max280-319 W (106-120%)
Z6 Anaerobic320-399 W (121-150%)

Step-by-step

FTP ≈ 20-min average × 0.95.
FTP = 280 × 0.95 = 266 W.
Power zones derived from FTP (Coggan 7-zone model).

How to use this calculator

Warm up 20 minutes, including 3 × 1-min hard efforts.
Do a 5-min all-out effort to clear anaerobic stores.
Recover 10 min, then ride 20 min as hard as evenly sustainable.
Average power × 0.95 = FTP.

About this calculator

FTP (Functional Threshold Power) is the highest power a cyclist can sustain for ~1 hour. The 20-minute test (after a 5-minute all-out warmup blow-off) is the practical proxy: pace yourself even, average for 20 minutes, multiply by 0.95. The 0.95 factor accounts for the fact that 20 min has more anaerobic contribution than 60 min. Once you have FTP, you can derive 7 power zones (Coggan) for structured training — Z2 endurance, Z4 threshold, Z5 VO2, etc.

Frequently asked

20-min power has more anaerobic contribution than a true 60-min effort. The 0.95 factor approximates the drop. Strong anaerobic riders use 0.93; pure aerobic use 0.97.