What is Cycling Wattage?
Cycling wattage is the power you produce with your legs to propel your bike forward. It is measured in watts (W) and is considered the ultimate measure of a cyclist's performance. The more power you can sustain, the faster you go.
Our cycling wattage calculator is based on the physics model from the paper "What is slowing me down? Estimation of rolling resistances during cycling". It breaks down the total power into four resistive components:
The Cycling Power Formula
The total cycling power is calculated as:
P = (Fg + Fr + Fa) × v / (1 − loss)
- P — Your power output (Watts)
- Fg — Gravity force (uphill resistance)
- Fr — Rolling resistance force
- Fa — Aerodynamic drag force
- v — Speed in m/s
- loss — Drivetrain power loss fraction
Component 1: Gravity (Fg)
When cycling uphill, you must overcome gravity. On a descent, gravity helps you accelerate. The gravity force is:
Fg = g × (m_rider + m_bike) × sin(arctan(grade / 100))
Where g = 9.80665 m/s² and grade is the slope in percent (e.g., 5 for 5% incline).
Component 2: Rolling Resistance (Fr)
Rolling resistance is caused by the tire deforming as it rolls over the surface. Smoother (slick) tires on smooth pavement produce very little rolling resistance, while knobby mountain bike tires on dirt produce much more.
Fr = Crr × g × (m_rider + m_bike) × cos(arctan(grade / 100))
Typical Crr (rolling resistance coefficient) values:
- Slick road tires (smooth asphalt): 0.004
- Standard road tires: 0.005
- Gravel / hybrid tires: 0.007
- Mountain bike tires: 0.012
- Off-road / knobby tires: 0.020
Component 3: Aerodynamic Drag (Fa)
Air resistance grows with the square of speed — doubling your speed quadruples the drag. Your riding position dramatically affects drag through the CdA value (drag coefficient × frontal area).
Fa = 0.5 × CdA × ρ × (v + v_wind)²
Typical CdA values by position:
- Triathlon / TT aero bars: 0.20
- Road bike — on the drops: 0.25
- Road bike — on the hoods: 0.32
- Road bike — upright / tops: 0.37
- Mountain bike — upright: 0.55
Air density (ρ) is taken as 1.225 kg/m³ (sea level, 15°C). Wind speed adds to or subtracts from your effective air speed: a headwind increases drag, a tailwind reduces it.
Component 4: Drivetrain Power Loss
Not all the power your legs produce reaches the wheel. A typical chain drive loses about 2–4% of power to friction. Dirty, worn, or poorly lubricated drivetrains can lose more. This is accounted for by dividing the mechanical power by (1 − loss/100).
Interpreting Your Result
Use watts per kilogram (W/kg) to compare cyclists regardless of body size:
- < 1.5 W/kg — Untrained / Beginner
- 1.5–2.5 W/kg — Fair
- 2.5–3.2 W/kg — Moderate (recreational cyclist)
- 3.2–4.0 W/kg — Good (enthusiast)
- 4.0–5.0 W/kg — Very Good (trained)
- > 5.0 W/kg — Exceptional (elite / pro)
Bonus: Calories Burned
To estimate calories burned, we use the mechanical efficiency of the human body (~24%). The formula is:
Calories (kcal) = Power (W) × 3.585 × Duration (hours)
This gives you the gross caloric expenditure including resting metabolism.
FAQs
What is a good watts per kg for cycling?
For recreational cyclists, 2.5–3.2 W/kg is a solid goal. Competitive amateur riders typically achieve 3.2–4.0 W/kg, and professional cyclists often exceed 5.0 W/kg in sustained efforts.
Does wind affect cycling power significantly?
Yes, dramatically. Because aerodynamic drag grows with the square of speed, a strong headwind can require 50–100% more power compared to calm conditions at the same speed.
How much power do I save by switching from knobby to slick tires?
On smooth pavement, switching from knobby mountain bike tires (Crr ≈ 0.020) to slick road tires (Crr ≈ 0.004) can reduce rolling resistance power by 75–80%, which translates to a significant reduction in total power required at moderate speeds.
Why does going downhill still require some power?
Even on a descent, rolling resistance and aerodynamic drag still act against you. Only at steep enough grades does gravity more than compensate — at that point, gravity force exceeds the resistive forces and you can freewheel or even brake.
What is the effect of body position?
At 30 km/h (~19 mph), switching from an upright MTB position (CdA 0.55) to a TT aero tuck (CdA 0.20) can cut aerodynamic drag power in half, saving 30–50 watts depending on conditions.