What FTP is
FTP is usually described as the highest power a rider can sustain in a quasi-steady state for about an hour. It is a practical anchor rather than a precise physiological boundary: it gives every rider a personal reference so that a target like “95% of FTP” means a comparable effort for different people.
Estimating FTP
Riders rarely ride all-out for an hour to find it. Common estimates include:
- 20-minute test — ride a well-paced, maximal 20 minutes after a thorough warmup; FTP is commonly estimated as about 95% of that average power.
- Race or hard-effort data — sustained power from recent hard efforts of a similar length.
- Ramp tests — short, step-increasing tests used by many training apps; the conversion to FTP varies by protocol.
Whichever method you use, use it consistently, and re-estimate when training clearly feels easier or harder than intended.
From FTP to zones
Zones divide the range of power into bands with different training purposes. SurgeIQ Lab uses six levels as a percentage of FTP:
| Zone | % of FTP | Typical use |
|---|---|---|
| Z1 Recovery | < 55% | Very easy spinning: recovery rides, and the easy half of interval sessions. |
| Z2 Endurance | 55–75% | Long steady riding; the bulk of most endurance training time. |
| Z3 Tempo | 75–90% | Sustained, moderately hard efforts; the upper part is often called "sweet spot". |
| Z4 Threshold | 90–105% | Efforts around FTP, typically in blocks of about 8–20 minutes. |
| Z5 VO2max | 105–120% | Hard intervals of roughly 3–8 minutes with similar recovery. |
| Z6 Anaerobic | 120–150% | Short, very hard efforts of seconds to about two minutes. |
Using zones in workouts
Workouts written in percentages scale automatically. With an FTP of 250 W, “5 min at 105–110% FTP” is 263–275 W; with an FTP of 200 W it is 210–220 W. SurgeIQ Lab keeps targets as percentages and only converts to watts for display or for formats that require absolute watts. FIT workout files store percentages directly, so a Garmin Edge applies the FTP set on the device — keep that in step with the FTP you train with (more on FIT).
Watts per kilogram
Dividing FTP by body weight gives watts per kilogram (W/kg), which matters most when climbing. It is useful for comparing your own fitness over time; it says little on its own about flat-road or time-trial speed, where aerodynamics dominate. The climb calculator shows how W/kg turns into time on a real climb.
Limitations
- FTP estimates carry error; a few percent either way changes every zone.
- Zone edges are conventions. 74% and 76% of FTP are not meaningfully different efforts.
- Short efforts depend on more than FTP; two riders with the same FTP can differ a lot over 30 seconds.
- Fatigue, heat and altitude change how a given power feels. Heart rate and perceived effort add useful context.
Where to go next
How this guide was written
Zone boundaries on this page are the ones SurgeIQ Lab uses in the app and in the power zone calculator, so the numbers match what you see after signing in.
Sources
- Allen, H. & Coggan, A. — Training and Racing with a Power Meter (VeloPress) — origin of the FTP concept and the power-level system these zones follow