Bike Gear Inch & Ratio Calculator

Gear inches represent the equivalent wheel diameter of a penny-farthing bicycle that would travel the same distance per pedal revolution. It's calculated as: Gear Inches = (Chainring Teeth ÷ Cog Teeth) × Wheel Diameter (inches). A higher gear inch number means a harder gear that goes farther per pedal stroke—ideal for speed on flat terrain. Lower gear inches mean easier pedaling for climbing. For example, a 50×15 gear on 27″ wheels gives ~90 gear inches, while a 34×28 climbing gear gives ~33 gear inches.

The gear ratio is simply the number of chainring teeth divided by the number of cog teeth: Gear Ratio = Chainring ÷ Cog. A ratio of 3.33 (e.g., 50÷15) means the rear wheel spins 3.33 times for every crank revolution. This raw ratio doesn't account for wheel size, which is why gear inches (ratio × wheel diameter) provides a more complete picture across different bikes.

For steep climbs (8%+ grade), aim for 25–35 gear inches. Moderate hills (4–7%): 35–50 gear inches. Most road bikes with a compact crankset (50/34) and an 11-28 cassette offer a low gear around 32–34 gear inches—adequate for most climbs. Ultra-endurance riders and loaded tourers often go as low as 20–25 gear inches using sub-compact cranksets (46/30) or wide-range cassettes.

Gear inches are directly proportional to wheel diameter. A 29″ MTB wheel produces ~11% higher gear inches than a 26″ wheel with the same drivetrain. This is why 29ers often run smaller chainrings. Similarly, wider tires increase the effective diameter slightly—a 700c×32mm tire has about a 27″ diameter versus ~26.5″ for a 700c×25mm. Our calculator accounts for these differences with preset tire sizes.

Most cyclists are most efficient at 80–100 RPM. Professional racers often sustain 90–110 RPM. For climbing, 70–85 RPM is common. Spinning too slowly (<60 RPM) increases knee strain and muscular fatigue, while excessively high cadence (>120 RPM) wastes energy. Use our speed table to find the cadence that matches your target speed for any gear combination.

Gear inches is the imperial measurement (used in the US and UK), while meters development is the metric equivalent popular in Europe. Meters development tells you exactly how many meters the bike travels per crank revolution: Meters Dev = Gear Inches × π × 0.0254. It's arguably more intuitive—a 7.1m development means each pedal stroke propels you 7.1 meters forward.

Road bikes: High gear typically 108–130 gear inches (53×13 or 50×11 on 27″), low gear 32–40 gear inches (34×28). Mountain bikes: High gear around 70–90 gear inches (32×10 on 29″), low gear as low as 16–22 gear inches (32×51 on 29″). Gravel bikes sit in between: high 100–115″, low 25–35″. Our combination table lets you compare any setup.

Start by identifying your lowest needed gear for the steepest climbs you regularly face. Use this calculator to model different chainring and cassette combinations. Aim for a low gear that lets you maintain at least 70 RPM on your toughest climbs. Then check the high gear—ensure you won't spin out on descents (most riders are comfortable up to 110–120 gear inches for sustained pedaling). The combination table is perfect for comparing setups side-by-side before buying new components.