Chainring/Cog Combo Calculator

How It Works

The Chainring/Cog Combo Calculator helps you find the ideal gear combination (front chainring and rear cog sizes) to achieve a specific speed at your preferred cadence on your bike. This is essential for matching your gearing to terrain and riding style, ensuring you can maintain efficient pedaling without spinning out or grinding in too-low gears.

The Formula

Variables

• Target Speed — Your desired cruising or working speed in kilometers per hour (km/h) — typically 20–40 km/h for road cycling, 15–30 km/h for gravel, and 10–25 km/h for mountain biking.
• Target Cadence — Your preferred pedaling rate in revolutions per minute (rpm) — most cyclists feel efficient at 85–95 rpm, though some prefer 70–80 rpm for climbing or 100+ rpm for sprinting.
• Wheel Circumference — The total distance the wheel travels in one complete rotation, measured in millimeters (mm). Common values: 2,100 mm (700c road), 2,050 mm (650b gravel), 2,300 mm (29-inch MTB).
• Chainring Teeth — The number of teeth on your front chainring(s) — road bikes typically have 50–53 teeth, gravel 38–46 teeth, and MTBs 30–36 teeth.
• Cog Teeth — The number of teeth on your selected rear cassette sprocket — smaller cogs (11–15 teeth) are for climbing and hard efforts, larger cogs (28–42 teeth) are for climbing and lower speeds.
• Bike Type — Your bicycle category: 1 = Road (drop bars, thin tires), 2 = Gravel (wider tires, mixed terrain), 3 = Mountain Bike (suspension, technical terrain).

Worked Example

Let's say you're a road cyclist aiming to maintain 32 km/h at a cadence of 90 rpm on a 700c wheel (circumference 2,100 mm). Using the formula: Chainring / Cog = (32 × 1,000,000) / (2,100 × 90 × 60) = 32,000,000 / 11,340,000 ≈ 2.82. This suggests you need a gear ratio of about 2.82, which could be achieved with a 50-tooth chainring and an 18-tooth cog (50 ÷ 18 = 2.78). At 90 rpm, this combination would propel you forward at approximately 31–32 km/h, making it ideal for steady-state road riding or a moderate group ride.

Practical Tips

• Match your gearing to terrain before the ride: if you're climbing steep hills, choose a smaller chainring or larger rear cog to maintain a comfortable 80–90 rpm; for flat roads, a larger chainring or smaller rear cog lets you carry speed with less effort.
• Your cadence preference matters more than speed alone — if you naturally pedal at 85 rpm, enter that value rather than forcing 100 rpm, because uncomfortable cadences cause fatigue and injury over time.
• Check your bike's compatibility: road bikes typically accept chainrings from 39–56 teeth and cogs from 11–32 teeth, while MTBs often use 28–42 tooth cogs for more climbing range; mixing mismatched components can cause chain drops and poor shifting.
• Use this calculator to plan gear upgrades: if you're struggling on climbs, try a larger rear cog (30–36 teeth) before replacing the entire crankset, since a cassette swap is cheaper and easier than swapping cranksets.
• Test your chosen combo during a short ride before committing to a full upgrade — a gear ratio that works on paper may feel sluggish or too spiky in real riding due to wind, fatigue, and terrain variation.

Last updated: March 10, 2026 · Reviewed by the BikeCalcs Editorial Team