bicycle speed and power calculator

This calculator is a powerful tool for analyzing cycling performance, planning races, and optimizing equipment. It calculates the Power (Watts) required to overcome all forces – gravity, rolling resistance, and air drag – to maintain a specific speed.

Who This Calculator Is Useful For

This tool is indispensable for anyone looking to connect their physical effort (power output) with their resulting speed, especially when facing varied terrain and equipment choices.

• Cyclists and Triathletes:
  • Pacing and Training: Determine the target Wattage needed to maintain a specific speed on a race course with known gradients. This helps set accurate training goals.
  • Performance Analysis: Understand where your power goes (e.g., if you’re losing more power to drag vs. gravity).¹
• Bike Mechanics and Equipment Optimizers:
  • “What If” Scenarios: Compare the performance gains from equipment changes, such as:
    • How much faster will I go for the same power if I lower my CdA (get into an aero position)?
    • How many Watts can I save by using lower Crr tires?
• Coaches and Analysts:
  • Prescribing Workouts: Create specific power targets for athletes based on the demands of an upcoming race course.

How to Use the Calculator

The calculator works by reading your inputs and running them through the core physics equation of cycling. Follow these steps to get an accurate result:

Step 1: Select Your Units

Use the switch at the top to toggle the inputs between Metric and Imperial .

Step 2: Input Your Basic Variables

Input Field	Description	Key Considerations
Target Speed	The speed you want to maintain.	Input in the chosen units (km/h or mph).
Total Mass	The mass of the Rider + Bike + all Gear.	Ensure this is your total system weight. Input in kg or lbs.
Gradient (Slope)	The steepness of the road.	Input as a percentage (e.g., enter 5 for a 5% uphill slope, -2 for a 2% downhill).

Step 3: Input Your Resistance Variables

These variables quantify the friction and air resistance you must overcome. Understanding these is key to using the calculator effectively.

1. Aerodynamic Drag Area ($CdA$)

This is the single most important factor on flat roads. It combines your Drag Coefficient (C_d) with your Frontal Area (A).

Position	Typical CdA Value (m2)
Upright/Hands on Tops	approx 0.35 – 0.45
Hands on Hoods/Drops	approx 0.28 – 0.35
Aerobars (Time Trial)	approx 0.20 – 0.26

2. Rolling Resistance Coefficient (Crr)

This represents the friction between your tires and the road surface. Lower is better.

Tire/Surface	Typical Crr Value
High-end race tires (smooth road)	approx 0.0035 – 0.005
Standard road tires	approx 0.006 – 0.008
Gravel or low-pressure tires	approx 0.01 – 0.015

Step 4: Calculate and Analyze

1. Click the “Calculate Watts” button.
2. The result box will display the Power at Crank (Watts) required to sustain the entered speed under the specified conditions.
3. Analyze: Change one input variable (e.g., reduce CdA from 0.35 to 0.25) and recalculate to see the immediate Wattage saving. This shows the practical benefit of optimizing your equipment or position.