Power-to-weight in one number
Cyclists are ranked by watts per kilogram (W/kg) — your sustainable power divided by your bodyweight. It is the single most useful number for predicting climbing performance, because on a gradient you are working against gravity acting on your total mass. This calculator takes your FTP and weight and returns your threshold W/kg plus the category band you fall into.
How it works
The formula is simply:
W/kg = FTP (watts) / bodyweight (kg)If you enter weight in pounds it is converted with 1 kg = 2.20462 lb before dividing. The result is mapped onto commonly used threshold-power category bands:
- Under 2.0 — Cat D, untrained / new rider
- 2.0 to 3.1 — Cat C, recreational
- 3.1 to 4.0 — Cat B, club racer
- 4.0 to 5.0 — Cat A, strong amateur
- 5.0 and above — elite / professional
These thresholds match the guidance popularised by Zwift and TrainerRoad for sorting riders by ability.
Why W/kg matters more than raw watts for climbing
On a flat road, a heavier rider with higher raw watts can easily outpace a lighter rider with lower absolute power — aerodynamics and raw force dominate. But on a climb, the equation changes fundamentally. The force you must overcome is gravity acting on your total system mass (rider plus bike). Power available at the pedals divided by that mass gives the acceleration up the slope, which is why two riders with identical W/kg will reach the summit at the same time regardless of their absolute weights.
This is also why professional cyclists dedicate enormous effort to staying at low body weight during the race season. A reduction of 2 kg in a 70 kg rider raises W/kg by about 2.9% at constant FTP, which translates directly to faster climbing. The effect is symmetric: a 2 kg gain at constant FTP drops W/kg by the same proportion.
The two routes to improving W/kg
Raising FTP — Structured training at and near your threshold zone is the primary driver. Intervals at 91 to 105% of FTP (Zone 4 in the Coggan model) are the most efficient stimulus for raising your sustainable one-hour power. VO2 max intervals (Zone 5) raise the ceiling, which gives the threshold training more room to grow into. A dedicated 8 to 12 week training block focused on these zones typically produces meaningful FTP gains.
Reducing body weight — Only body weight that can be safely lost improves W/kg; losing muscle mass and dropping FTP at the same time is counterproductive. Riders who successfully improve W/kg through weight change typically work with a sports dietitian to reduce excess body fat while maintaining training load and recovery.
Both levers interact: more training raises FTP but may not reduce weight; caloric restriction can reduce weight but risks under-fuelling training. The most durable W/kg improvements come from combining progressive training load with adequate nutrition.
Worked example
A 75 kg rider with an FTP of 280 W has 280 / 75 = 3.73 W/kg, placing them in Cat B. To climb with the Cat A group they would need roughly 300 to 320 W at the same weight (4.0 to 4.27 W/kg), or the same 280 W at about 70 kg (4.0 W/kg). The two paths to Cat A are equivalent in outcome but very different in training focus.
Always test FTP on the same kind of effort (ramp test or 20-minute field test) so comparisons over a season stay consistent. Re-measure every 6 to 8 weeks during a structured training block.