Riding a bike means fighting gravity, tyre rolling resistance and air drag. On the flat above about 25 km/h, air drag dominates, which is why aero positions matter so much. On a climb, weight takes over.
How to use the Cycling Power Calculator
- Rider weight
- Bike and gear weight
- Speed
- Riding position (CdA)
- Custom CdA (m²)
- Tyres and surface (Crr)
- Drivetrain condition
- Headwind (negative = tailwind)
- Gradient (%)
- Elevation
- Ride duration
Results update as you type, every field has its own unit menu, and everything is calculated in your browser.
How it works
Enter your weight and the bike weight, speed, position, tyres and surface, drivetrain condition, headwind, gradient, elevation and ride duration.
Inputs explained
| Field | What to enter |
|---|---|
| Rider weight | Units: kg, lb |
| Bike and gear weight | Units: kg, lb |
| Speed | Units: km/h, mph, m/s |
| Riding position (CdA) | Choose one: Upright (city bike), Tops of the bars, Hoods, Drops … |
| Custom CdA (m²) | A number |
| Tyres and surface (Crr) | Choose one: Road tyres on smooth asphalt, Road tyres on rough asphalt, Gravel tyres on gravel, MTB knobby tyres on trail … |
| Drivetrain condition | Choose one: Well-maintained, clean (3%), Average (4%), Dirty / worn (5%), Fixed gear / single speed (1.5%) |
| Headwind (negative = tailwind) | Units: km/h, mph, m/s |
| Gradient (%) | A number |
| Elevation | Units: m, ft |
| Ride duration | Units: min, h |
What each result means
- Air density = 1.225×exp(-0.00011856×[Elevation])
- Power to climb = [m]×9.80665×sin([th])×[Speed]÷(1 – [Drivetrain condition])
- Power for rolling resistance = [m]×9.80665×cos([th])×[Tyres and surface (Crr)]×[Speed]÷(1 – [Drivetrain condition])
- Power for air drag = 0.5×[Air density]×[CdA]×([Speed] + [Headwind (negative = tailwind)])×abs([Speed] + [Headwind (negative = tailwind)])×[Speed]÷(1 – [Drivetrain condition])
- Total power needed = max(0, [Power to climb] + [Power for rolling resistance] + [Power for air drag])
- Power-to-weight = [Total power needed]÷[Rider weight]
- Work done = [Total power needed]×[Ride duration]×60÷1000
- Calories burned (24% efficiency) = [Total power needed]×[Ride duration]×60÷4184÷0.24
Example values
How the main result changes when Rider weight changes and everything else stays at the example values above:
| Rider weight (kg) | Total power needed (W) |
|---|---|
| 37.5 | 134 |
| 56.25 | 140 |
| 75 | 147 |
| 93.75 | 153 |
| 112.5 | 159 |
| 150 | 172 |
Formula
P = (F_gravity + F_rolling + F_drag) × v ÷ (1 − loss)
F_gravity = m·g·sin θ, F_rolling = m·g·cos θ·Crr, F_drag = ½·ρ·CdA·(v + v_wind)², ρ = 1.225·e^(−0.00011856·h)
Worked example
Inputs: Rider weight: 75 kg; Bike and gear weight: 9 kg; Speed: 30 km/h; Riding position (CdA): Hoods; Tyres and surface (Crr): Road tyres on smooth asphalt; Drivetrain condition: Well-maintained, clean (3%); Headwind (negative = tailwind): 0 km/h; Gradient (%): 0; Elevation: 0 m; Ride duration: 60 min.
Results: Air density = 1.225 kg/m³; Power to climb = 0 W; Power for rolling resistance = 28 W; Power for air drag = 118 W; Total power needed = 147 W; Power-to-weight = 1.96 W/kg; Work done = 528 kJ; Calories burned (24% efficiency) = 526 kcal.
Key terms
- CdA
- Drag area (m²).
- Crr
- Coefficient of rolling resistance.
Frequently asked questions
How many watts does a typical rider produce?
100–200 W for an hour; pros hold 350–450 W.
Why does speed matter so much?
Drag power rises with the cube of speed.
What is CdA?
Drag coefficient × frontal area (your "aero" size).
How accurate is this?
Within about 5–10% if the inputs are realistic; a power meter is exact.