Cycling Power Calculator

Cycling power output in watts is the gold standard of cycling performance measurement. Unlike speed (affected by wind and terrain) or heart rate (affected by fatigue and caffeine), power directly measures mechanical work output and is reproducible across any conditions.

Power formula: P = F × v

Where:

• P = power in watts (W)
• F = force applied to the pedals (Newtons)
• v = velocity of the foot/crank (m/s)

In cycling terms: P = Torque × Angular Velocity P = (Force × Crank Length) × (2π × Cadence ÷ 60)

Simplified practical formula: P (watts) = F × Crank Length (m) × Cadence (RPM) × 2π ÷ 60

Speed from power (on flat, no wind): v³ ≈ P ÷ (0.5 × ρ × CdA + Crr × m × g / v)

For rough estimation: Speed ≈ (P ÷ CdA)^(1/3) where CdA is the aerodynamic drag area.

What each variable means:

• Watts: the unit of power; 1 watt = 1 joule of energy per second
• Cadence (RPM): pedal revolutions per minute; most efficient range is 85–100 RPM for trained cyclists
• CdA (Cd × Frontal Area): aerodynamic drag coefficient; aggressive road position reduces CdA significantly vs. upright riding
• Crr: coefficient of rolling resistance; varies by tire pressure, width, and road surface
• FTP (Functional Threshold Power): the power you can sustain for ~1 hour; the standard baseline for training zones

Reference: power-to-weight ratio benchmarks (W/kg at FTP):

• 1.0–1.5 W/kg: Untrained recreational
• 2.0–2.5 W/kg: Recreational cyclist
• 3.0–3.5 W/kg: Cat 4 racer / sportive rider
• 3.5–4.5 W/kg: Cat 2–3 racer / amateur competitive
• 4.5–5.5 W/kg: Elite amateur / Cat 1
• 5.5–6.5 W/kg: Professional continental
• 6.5+ W/kg: Tour de France contender

Worked example: Rider: 75 kg, FTP 285W. Riding 40km at 240W average (84% of FTP).

• Power-to-weight ratio = 285 ÷ 75 = 3.8 W/kg (competitive amateur)
• Intensity factor = 240 ÷ 285 = 0.842 (84.2%)
• Duration: 40km at ~36 km/h average ≈ 67 minutes
• Training Stress Score (TSS) ≈ 67 × 0.842² × 100 ÷ 60 = 79 TSS (moderate training load)

Crr (rolling resistance) varies a lot by tire

The Crr value plugged into the power formula has a huge effect on total wattage. Real-world values:

Doubling Crr from 0.004 to 0.008 (swapping a road tire for an aggressive gravel one) adds roughly 25 watts at 30 km/h on flat ground for a 75 kg rider. That’s enough to drop you from a Cat 3 paceline to off the back.

Wind matters more than gradient on flat ground

Aerodynamic drag scales with velocity cubed (P ∝ v³). The relevant velocity is your speed relative to the air, not over the ground. With a 20 km/h headwind, a 30 km/h ground speed produces drag equivalent to 50 km/h still-air riding. The full formula:

P_air = 0.5 × ρ × CdA × (v + v_wind)² × v

That headwind doesn’t just slow you down; it dramatically inflates the power required to maintain the same ground speed. This is why power-based pacing is more reliable than speed-based pacing for outdoor riding.