FTP calculation

How precise is this FTP test?

The outcomes of these FTP calculations are as accurate as the input. The physics behind this equation is 100% exact, but to come to an outcome we have to make assumptions.

The biggest resistance on the flat is the air resistance. For that, it is important to know the frontal surface and how easy the air detaches from the cyclist and the bike. Therefore, it makes a difference if you sit up straight or in a time trial position or if you wear a normal helmet or a time trial helmet. This value is expressed as CdA (drag coefficient times frontal area) and can only be measured precisely in a wind tunnel.

With this calculation, we estimate this CdA value based on length, weight, type of bike, and position. Especially with these estimates, there can be quite a difference and the higher the speed, the bigger the possible error.

Besides that, we make certain assumptions about the rolling resistances and even the air density based on the temperature. Therefore, use this calculator as a rough estimation only of your FTP. If you really want to take this to the next level, then buy a power meter and do an exercise test in a performance lab.