Health⏱ 6 min read
How to Calculate Cycling Power Output and FTP
Power (watts) is the most accurate measure of cycling performance. Here's how to calculate power from speed and gradient, how to estimate your FTP, and how it compares to heart rate training.
Cycling power is the gold standard of performance measurement — unlike speed (affected by wind and gradient) or heart rate (which lags and varies with temperature, fatigue, and caffeine), power directly measures mechanical work output.
What Power Measures
Power (Watts) = Force (Newtons) x Velocity (m/s)
In cycling: the force you apply to the pedals combined with
cadence (how fast you pedal) determines watts.
Power-to-weight ratio (W/kg) = Watts / Body weight (kg)
This is the key metric for climbing performance.
W/kg benchmarks (sustained 20 minutes):
Recreational cyclist: 2.0-3.0 W/kg
Trained amateur: 3.0-4.0 W/kg
Elite amateur/masters: 4.0-5.0 W/kg
Professional cyclist: 5.5-6.5 W/kg
Estimating FTP (Functional Threshold Power)
FTP = the highest average power you can sustain for 60 minutes.
20-minute test protocol (most common):
1. Warm up 15-20 minutes with effort escalation
2. Ride 20 minutes at maximum sustainable effort
3. Record average watts
FTP estimate = Average 20-min watts x 0.95
(You can sustain slightly less for 60 minutes vs 20 minutes)
Example: 20-minute average = 250 watts
FTP = 250 x 0.95 = 237.5 watts
For a 70kg rider: W/kg = 237.5 / 70 = 3.39 W/kg (solid trained amateur)
Training Zones Based on FTP
Zone% of FTPPurpose
Zone 1 (Active recovery)Under 55%Recovery rides
Zone 2 (Endurance)55-75%Base fitness, long rides
Zone 3 (Tempo)76-90%Sustained effort, race pace
Zone 4 (Lactate threshold)91-105%FTP intervals
Zone 5 (VO2 max)106-120%Short hard intervals
Zone 6 (Anaerobic)121-150%Sprint intervals, very short
Estimating Power Without a Power Meter
On a climb: Power (W) can be estimated from speed and gradient
P = (m x g x v x sin(angle)) + (0.5 x Cd x A x rho x v^3)
(second term = air resistance — negligible on steep climbs)
Simplified for climbing (gradient above 5%):
P ≈ total mass (rider + bike) x 9.81 x speed (m/s) x gradient fraction
Example: 75kg rider + 9kg bike = 84kg total
Speed: 15 km/h = 4.17 m/s
Gradient: 7% = 0.07
P ≈ 84 x 9.81 x 4.17 x 0.07 = 241 watts
This estimate ignores rolling resistance and wind — typically
accurate within 10-15% for climbs above 5%.