Cycling Speed & Power Calculator: Convert Watts ↔ km/h

Optimize your pacing and compare your gear: our cycling calculator lets you estimate your expected speed (km/h) from your power output in watts — or calculate the watts you’ll need to hit a target time.

Perfect for fine-tuning your position, choosing the right tires, or building a pacing strategy for time trials and triathlon. Understand the physical limits before you’re on the start line.

Mode: Simple

A quick check on the go. Use predefined presets for aerodynamic drag (CwA), rolling resistance (Crr), and gradient. Perfect for first estimates.

Mode: Expert

Maximum accuracy for performance analysis. Includes air density (temperature/altitude/air pressure) as well as drivetrain efficiency.

Already know your aero losses in watts? Use our converter: Convert watts to Crr & CwA/CdA

How to use the simulator for your setup

01. Choose mode & goal

Decide whether you want to calculate speed from your power (watts) — or calculate the required watts the other way around. Enter your system weight (rider + bike + equipment) to set the baseline for rolling resistance and climbing power.

02. Presets or expert values

In Simple mode use our optimized presets for aero position (CdA) and rolling resistance (Crr). In Expert mode you can fine-tune the inputs and precisely simulate external factors such as air temperature and elevation.

03. Check power breakdown

In Expert mode analyze your results in more detail — how many watts go into aero drag, rolling resistance, or climbing. If you want to get even more precise, use TrackIQ to see where you’re gaining the most time on your course.

Aerodynamic drag (CdA) – your biggest enemy

On flat terrain, roughly 80–90% of your energy goes into pushing air out of the way. Because drag increases with the square of speed, the power required to overcome it rises with the cube. Doubling your speed therefore requires eight times the power.

Benchmark: A typical road cyclist riding in the drops has a CwA of around 0.30, while time-trial pros can get below 0.20. Every “milli-CdA” counts!

Rolling resistance (Crr) – the hidden brake

Rolling resistance is often underestimated because it increases linearly with speed. It’s driven by internal tire friction (hysteresis losses) and the road surface. High-quality casings and the right tire pressure can reduce this loss dramatically.

Fact: Switching from standard tubes to latex or tubeless often reduces Crr from 0.005 to 0.003. At 40 km/h, that saves about 12–15 watts — an upgrade that doesn’t cost you a single drop of sweat.

Gradient – where system weight dominates

Once the gradient exceeds about 5%, gravity becomes the dominant force. Aerodynamics moves into the background, and your watts-per-kilogram (W/kg) ratio determines your finish time.

TrackIQ insight: Our simulator helps you decide whether it’s worth “overpacing” on the climb to gain more time on the descent that follows — the classic question of optimal power distribution.

Drivetrain efficiency – mechanical losses

Not all the power from your legs makes it to the road. Your chain, jockey wheels, and bearings absorb energy. A clean, waxed drivetrain can reach up to 98% efficiency, while a dirty system can eat up to 5% of your power.

Example: If you’re putting out 300 watts, a poor efficiency costs you 15 watts in the drivetrain. That’s more than the advantage many aero wheelsets deliver.

Frequently Asked Questions (FAQ)

The calculator uses physics-based formulas to model the resistive forces. In Expert mode, it includes not only aerodynamic drag (CdA) and rolling resistance (Crr), but also air density (based on temperature, altitude, and air pressure) as well as mechanical drivetrain losses — for maximum accuracy.

CdA (or CwA) is the product of the drag coefficient (Cw) and frontal area (A). It’s the key metric for your aerodynamics. The lower the value, the less energy you need to fight the wind — especially important at speeds above 30 km/h.

System weight includes the rider, the bike, and all equipment. It directly affects rolling resistance and becomes the decisive factor on climbs because it determines the required lifting power (watts per kilogram). On flat terrain, weight is secondary compared to aerodynamics.

By simulating your setup with our calculator, you can see whether an aero position (lower CdA) or weight savings will gain you more time on your course. On top of that, the pacing strategy helps you distribute your power (watts) optimally across the route to avoid blowing up.