FTP Calculator

Functional Threshold Power (FTP) is roughly the highest power output you can sustain for about an hour. It's the reference number used to set training zones, pace races, and calculate metrics like Intensity Factor and Training Stress Score. Most power-based training and race planning starts with an accurate FTP.

Enter the distance and time from a ride you already completed, along with your body weight and riding position. The tool uses a physics model to back-solve the average power required to produce that speed, accounting for aerodynamic drag and rolling resistance. It then applies a duration-based intensity assumption to convert that average power into an estimated FTP.

This estimate is a rough starting point, not a substitute for a real FTP test. It assumes flat terrain, no wind, and a generic CdA based on riding position — real courses, weather, drafting, and pacing all shift the true number. A structured field test or a course-specific model with your actual measured CdA will always be more accurate.

Riding position is the biggest driver of aerodynamic drag (CdA) at any given speed. A rider tucked into an aero position on a TT bike faces significantly less air resistance than the same rider sitting upright on flat bars, so the same speed implies a very different power output — and therefore a different estimated FTP — depending on position.

You can use any steady, reasonably hard effort — a time trial, a hard group ride segment, or a structured test. The estimate gets less reliable for rides with a lot of coasting, stops, or highly variable effort, since the model assumes a fairly consistent power output across the ride.

This tool solves the physics equation in reverse — estimating power and FTP from a known speed. Best Bike Split's race pacing plans work the other direction: starting from your real FTP and course data (elevation, wind, your measured aerodynamics) to build a segment-by-segment power target for an upcoming race.