Cycling Gear Calculator: Speed, Cadence & Gear Inches

A cycling gear calculator works out the gear ratio, gear inches, and speed you get for a given chainring, cassette sprocket, wheel size, and cadence. You enter the number of teeth on the front chainring and rear sprocket, your wheel diameter, and your pedaling cadence, and it returns the distance traveled per pedal stroke and the resulting speed. This helps you compare gearing setups, plan for hills or flats, and understand how changing components affects your ride.

Formula

The core relationship is simple: each full pedal crank revolution turns the rear wheel a number of times equal to the chainring teeth divided by the cassette teeth.

Gear ratio = Chainring teeth ÷ Cassette teeth

Gear inches = Gear ratio × Wheel diameter (in inches)

Development (meters per crank revolution) = Gear ratio × Wheel circumference

Speed = Development × Cadence × 60 ÷ 1000 (to get km/h)

Where:

• Chainring teeth (t): number of teeth on the front crank ring, typically 34–53
• Cassette teeth (r): number of teeth on the rear sprocket, typically 11–34
• Wheel diameter (w): actual outer tire diameter in inches, not rim size (a 700c rim with a 28mm tire is about 27.5 inches total)
• Cadence (c): pedal revolutions per minute, typically 70–100
• Wheel circumference = diameter × Ï€ (3.14159)

Worked Example

Using the defaults: 50-tooth chainring, 15-tooth cassette, 27.5-inch wheel, 90 rpm cadence.

1. Gear ratio = 50 ÷ 15 = 3.33
2. Wheel circumference = 27.5 × 25.4 = 698.5 mm (converting inches to mm), then × π = 2194.6 mm = 2.1946 m
3. Development = 3.33 × 2.1946 = 7.32 meters per crank revolution
4. Speed = 7.32 m × 90 rpm × 60 min = 39,528 m/h = 39.5 km/h

The calculator shows 39.5 km/h, matching this step-by-step result. Gear inches come to 3.33 × 27.5 = 91.7 inches.

Why Gear Inches Still Matter

Gear inches is a traditional way to describe how “hard” or “easy” a gear feels. A higher gear inch number means more distance per pedal stroke, which is harder to accelerate but faster at high cadence. A lower number means easier spinning, good for climbing. The system dates to the penny-farthing era, where the wheel was the chainring, but it remains useful today because it normalizes different wheel sizes. A 50/15 on a 27.5-inch wheel gives 91.7 gear inches; the same gears on a 29-inch wheel give 96.7 gear inches — a meaningful difference in feel.

For a more modern comparison, many riders use development (meters per revolution) instead, since it directly relates to the ground you cover. The calculator provides both, so you can use whichever matches your mental model.

How to Choose the Right Gearing

There is no single “best” gear setup — it depends on terrain, fitness, and riding style. Use the calculator to compare options before buying parts.

• Flats and racing: Look for a top gear around 100–110 gear inches, typically a 52/11 or 53/12, to maintain speed at 100+ rpm without spinning out.
• Mixed terrain: A compact crankset (50/34) with an 11–28 cassette gives a wide range: about 33 gear inches low for climbs and 100+ high for descents.
• Mountain biking: Aim for a low gear under 20 gear inches for steep technical climbs, often a 30/42 or 32/50 combination.
• Touring with luggage: You need a very low gear, around 20–22 gear inches, to climb loaded hills at a sustainable cadence.

Test your current setup first: if you struggle to hold 80 rpm on climbs, you need a lower gear. If you spin out on descents, you need a higher one.

Common Mistakes and Misconceptions

The most frequent error is using rim diameter instead of actual wheel diameter. A 700c rim is 622 mm bead seat diameter, but with a 25mm tire the total is about 672 mm (26.5 inches). Using 700 mm or 27.5 inches for a 700c wheel will understate speed by roughly 4–5%. Always measure your tire’s outer diameter or use a manufacturer spec for the exact tire model.

Another mistake is confusing cadence with speed. Cadence is pedal rpm, not wheel rpm. The gear ratio converts one to the other. A 50/15 gear at 90 rpm gives about 39.5 km/h, but at 60 rpm it drops to 26.3 km/h — the same gear, very different speed.

Also, the calculator assumes no losses from drivetrain friction, wind, or rolling resistance. Real-world speed on flat ground will be lower than calculated, especially at higher speeds where air drag dominates. The calculated speed is a theoretical maximum for a steady cadence, not a prediction of what you’ll actually ride.

Units and Conversions

The calculator uses inches for wheel diameter because that is the standard in gear-inch tradition. If you measure your wheel in millimeters, divide by 25.4 to get inches. For speed, the output is in km/h; to convert to mph, divide by 1.609. Development is in meters; to get feet, multiply by 3.281.

For example, a 700×28c tire has a nominal diameter of about 28 mm × 2 + 622 mm = 678 mm = 26.7 inches. Entering 26.7 instead of 27.5 changes speed by about 3%, which is small but noticeable over a long ride.

Limits of the Calculator

This calculator is a pure mechanical model. It does not account for:

• Wind resistance, which grows with the square of speed
• Rolling resistance from tire pressure and surface
• Rider weight and bike weight
• Drivetrain efficiency (typically 95–98%, losing 2–5% to chain friction)
• Gradient — climbing requires far more power than this model suggests

Use the speed output as a relative comparison between gear setups, not as an absolute prediction. It is excellent for answering “which gear is faster at the same cadence?” but not for “how fast will I go on this route?” For that, you need power data and a bike computer with GPS.

Frequently Asked Questions

What is a good gear ratio for hills?
A ratio below 1.5 (e.g., 34/24) gives a low gear suitable for steep climbs. For loaded touring, go below 1.2. For moderate hills, 1.5–2.0 works. The calculator shows the ratio directly, so you can compare options.

How do I measure my wheel diameter?
Place your bike on a flat surface, mark the floor under the tire contact point, roll forward one full wheel revolution, and measure the distance between marks. Divide by π (3.14159) to get diameter in the same units. This accounts for tire width and pressure.

What cadence should I use?
Recreational riders often choose 70–80 rpm; experienced cyclists prefer 85–100 rpm. Lower cadence (60–70) is common for climbing or when tired. The calculator lets you test different cadences to see how speed changes.

Is gear inches the same as gear ratio?
No. Gear ratio is just teeth divided by teeth (a pure number). Gear inches multiplies that by wheel diameter, giving a distance-like value. Two bikes with the same gear ratio but different wheel sizes will feel different — gear inches captures that difference.

Why does my actual speed differ from the calculated speed?
Real-world speed is lower due to wind resistance, tire deformation, drivetrain friction, and the fact that you cannot maintain a perfectly constant cadence. On flat ground with no wind, expect 5–10% lower than calculated. On climbs, the difference can be 30% or more.

Can I use this for a single-speed or fixed-gear bike?
Yes. Enter your single chainring and single cog. For fixed gear, you also need to consider that you cannot coast, so gear choice affects braking and descending comfort — a lower gear makes it harder to control speed on descents because your legs must spin faster.

Related

• Calculator Net Mileage: How to Work It Out
• Cadence Calculator VDC: What It Is & How to Use
• Cadence Calculator: Find Your Running Cadence

in t | Chainring teeth | teeth | 50 | 0
in r | Cassette teeth | teeth | 15 | 0
in w | Wheel diameter | inches | 27.5 | 0
in c | Cadence | rpm | 90 | 0
out speed | Speed | km/h | (t / r) * (w * 25.4 * pi / 1000) * (c * 60) / 1000 | 1
out gear_in | Gear inches | inches | (t / r) * w | 1
out ratio | Gear ratio | - | t / r | 2
out dev | Development | m | (t / r) * (w * 25.4 * pi / 1000) | 2