Bike Speed Calculator - Speed from Cadence and Gears
Use the bike speed calculator to find mph and km/h from cadence, chainring teeth, cog teeth, wheel size, and tire thickness for any gear setup.
Bike Speed Calculator
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What Is the Bike Speed Calculator?
A bike speed calculator turns your pedaling cadence, chainring and cog selection, and wheel size into a predicted riding speed in mph and km/h so you can plan a ride, pick a gear, or check your bike computer against what your legs are producing. Use it whenever you know the cadence you want to hold and want the speed it will deliver, or when you know the speed you need to hold and want the cadence that produces it. The same inputs feed both directions because the relationship between cadence, gear ratio, and wheel size is reversible.
- • Road cyclists planning endurance pace: Confirm that a target 90 RPM cadence on a 50x17 gear delivers the 20 to 22 mph cruise speed you want on the flats.
- • Mountain bikers sizing a climbing gear: Match a 28x36 climbing gear to the 60 to 75 RPM cadence that keeps you seated on steep pitches.
- • Indoor trainers validating outdoor pacing: Translate a trainer cadence into the outdoor mph and km/h you will hold on a 700c or 29er wheel.
- • Commuters comparing e-bike and bike speed: Compare the speed a steady cadence produces on two bikes with different chainrings, cassettes, or wheel sizes.
Every output is recomputed from your inputs in real time, so adjusting the chainring, cog, wheel size, or cadence instantly refreshes the mph, km/h, gear ratio, and gear inches without leaving the form.
When the missing number is pedal RPM rather than speed, Bike Cadence Calculator runs the same chainring, cog, and wheel inputs to back-solve cadence from a known mph or km/h.
How the Bike Speed Calculator Works
The bike speed calculator uses the standard bicycle drivetrain relationship that links pedal speed, gear ratio, and rolling circumference. Enter the direction you want to solve and the calculator returns mph, km/h, and the supporting gear numbers in one step.
- cadence: Pedal revolutions per minute, the input the user enters when solving for speed.
- chainringTeeth: Number of teeth on the front chainring; combined with the rear cog to form the gear ratio.
- cogTeeth: Number of teeth on the selected rear cog from the cassette.
- wheelDiameter: Rim bead-seat diameter in inches (24.5 is a 700c or 29er, 23.0 is a 650b or 27.5 inch, 22.0 is a 26 inch MTB).
- tireThickness: Inflated tire thickness in millimetres; doubled internally to add to the rim diameter for the rolling diameter.
The same formula is reversible, so feeding in cadence returns the speed and feeding in a known speed returns the cadence that produced it.
50x17 gear at 90 RPM on a 700c rim with a 28 mm tyre
Cadence 90 RPM, chainring 50 teeth, rear cog 17 teeth, rim 24.5 in, tire 28 mm.
Rolling diameter 24.5 + 2 × (28 / 25.4) = 26.7 in. Circumference π × 26.7 × 0.0254 = 2.131 m. Gear ratio 50 / 17 = 2.94. m/min = 2.131 × 2.94 × 90 = 564. Speed = 564 × 0.06 = 33.8 km/h = 21.0 mph.
21.0 mph / 33.8 km/h at 90 RPM in a 50x17 gear on a 700c wheel.
That is a typical road race pace for a trained cyclist on the flats and a reasonable target for a fast group ride.
Compact 50x25 gear at 80 RPM on a 700c with a 25 mm tyre
Cadence 80 RPM, chainring 50 teeth, rear cog 25 teeth, rim 24.5 in, tire 25 mm.
Rolling diameter 24.5 + 2 × (25 / 25.4) = 26.47 in. Circumference π × 26.47 × 0.0254 = 2.112 m. Gear ratio 50 / 25 = 2.0. m/min = 2.112 × 2.0 × 80 = 337.9. Speed = 337.9 × 0.06 = 20.3 km/h = 12.6 mph.
12.6 mph / 20.3 km/h at 80 RPM in a 50x25 climbing gear on a 700c wheel.
That is a steady climbing pace for a road cyclist in a compact gear and matches what most riders see on 6 to 8 percent grades.
According to Wikipedia bicycle gear reference, the metres travelled per minute equal the wheel circumference multiplied by the chainring-to-cog ratio and the cadence in revolutions per minute.
If you want a full table of every gear's ratio, gear inches, and meters of development across the cassette, Bicycle Gear Ratio Calculator works through the same chainring and cog list in one pass.
Key Cycling Speed Concepts
Four ideas explain why the calculator behaves the way it does and what the speed number really means for cyclists on the road or trail.
Cadence as the input
Pedal cadence is revolutions per minute and is the input most cyclists can measure directly with a cadence sensor. The calculator treats cadence as the primary driver of speed.
Gear ratio
Gear ratio is the chainring tooth count divided by the rear cog tooth count. A 50x17 gear has a ratio of 2.94, so the rear wheel turns almost three times per pedal revolution.
Rolling circumference
Rolling circumference is the distance covered in one wheel revolution and equals pi times the rim diameter plus twice the tire thickness. A 700c rim with a 28 mm tyre has a circumference of about 2.13 metres.
Cadence-speed equivalence
Speed and cadence are linked by the same equation in either direction, so a known speed implies a cadence for the same gear, and a known cadence implies a speed. The calculator rearranges the equation.
To understand why the same speed feels easier for one rider than another, Cycling Power-to-Weight Ratio Calculator turns body weight and FTP into a watts-per-kilogram benchmark you can compare against.
How to Use This Calculator
The input order mirrors how a cyclist would read a cadence sensor and gear chart, so the calculator fits into a normal ride review without extra steps.
- 1 Choose the calculation direction: Pick 'Cadence → Speed' if you have a cadence reading and want mph and km/h, or 'Speed → Cadence' if you have a bike computer speed and want the implied RPM.
- 2 Enter the cadence or speed: Type the cadence in revolutions per minute, or the speed in miles per hour, depending on the direction you chose.
- 3 Enter the chainring and cog teeth: Type the teeth on the active chainring and the rear cog; road bikes often use 50x17, while mountain bikes use combinations like 32x18.
- 4 Enter the wheel diameter and tire thickness: Pick the rim bead-seat diameter in inches and the inflated tire thickness in millimetres.
- 5 Read the speed and gear panel: The primary result shows mph and km/h, and the secondary panel lists gear ratio, rolling circumference, gear inches, and meters of development.
For a Sunday road ride on a 50x17 gear at a steady 90 RPM, choose cadence-to-speed, enter 90 RPM, chainring 50, cog 17, rim 24.5 in, tire 28 mm, and read 21.0 mph / 33.8 km/h from the results panel, with a gear ratio of 2.94.
For race plans that start from a target pace per mile or kilometre, Bike Pace Calculator converts the speed from this calculator into minutes per mile and minutes per kilometre.
Benefits of Using This Calculator
These benefits show up most clearly when the calculator is used as a planning tool before a ride, not just as a curiosity afterwards.
- • Plan speed without doing the math at the trailhead: Pick a cadence you can hold and read the speed it will produce.
- • Pick the right gear before a climb: Compare gear ratios and predicted speeds for 50x17, 50x25, and 34x28 gears on the same wheel.
- • Convert between mph and km/h without losing accuracy: Switch between miles and kilometres using the exact 1.609344 factor.
- • Back-solve cadence from a target speed: Enter the speed you need to hold and read the cadence the calculator returns.
- • Diagnose mismatches between sensor and bike computer: Compare the predicted speed with the speed your bike computer reports to spot sensor dropouts.
Once you know the speed you will ride, Calories Burned Biking Calculator turns the same distance and time into an estimated calorie burn so you can plan fuelling and recovery.
Factors That Affect Your Bike Speed Result
Four factors move the predicted speed that the calculator reports, and understanding them helps decide when the result is a fair prediction and when the ride will trail the number.
Elevation gain and terrain
Hills, headwinds, and rough surfaces slow a rider far more than the rolling circumference suggests, so a hilly loop can drop average speed by 2 to 5 mph compared with a flat equivalent distance.
Tire size and pressure
Wider tires and lower pressures increase rolling resistance and raise the rolling diameter, so a 32 mm tyre at 60 psi is meaningfully slower than a 25 mm tyre at 90 psi.
Rider fitness and fatigue
Average cadence reflects how fresh the rider was at the start, so a tired rider drops cadence and therefore speed on a long ride.
Stop time and traffic
The calculator uses moving speed, so red lights and coffee stops reduce the average speed.
- • The math uses rolling circumference and gear ratio only, so it does not adjust for tire width, surface, or pressure. Treat the predicted speed as a flat-road benchmark.
- • The calculator assumes flat, calm conditions on a paved surface, so a headwind or a climb of more than 2 to 3 percent grade will produce a real-world speed lower than the number.
Treat the calculator's speed as a planning anchor rather than a promise, and adjust it for the specific route and conditions before race day.
According to Wikipedia cycling cadence reference, most road cyclists pedal between 70 and 100 RPM during steady cruising, with recreational riders often sitting closer to 70 to 80 RPM and trained racers near 90 to 100 RPM.
According to Wikipedia bicycle wheel reference, the rolling circumference of a bicycle wheel equals pi times the outside diameter of the rim plus twice the tyre thickness.
When you want to explain why one rider holds a faster speed than another at the same fitness, Cycling FTP Calculator estimates the functional threshold power that sets the ceiling for sustained effort.
Frequently Asked Questions
Q: How do you calculate bike speed from cadence and gear ratio?
A: Multiply the wheel rolling circumference by the chainring to cog ratio, then multiply by the cadence in revolutions per minute to get metres per minute. Convert metres per minute to km/h by multiplying by 0.06, and to mph by dividing the km/h value by 1.609344. The bike speed calculator runs all three steps in real time.
Q: What cadence do I need for 20 mph on a road bike?
A: A 50x17 gear on a 700c rim with a 28 mm tyre needs about 86 RPM to hold 20 mph, while a 52x19 gear on the same wheel needs about 78 RPM. The exact number depends on chainring, cog, rim size, and tire thickness, so the calculator lets you read the cadence for any gear setup.
Q: How does wheel size affect bike speed?
A: A larger rolling diameter covers more distance per wheel revolution, so at the same cadence and gear ratio a 29er wheel produces a higher speed than a 26 inch wheel. Always enter the rim bead-seat diameter plus twice the tire thickness for an accurate rolling circumference.
Q: How does gear ratio change bike speed at the same cadence?
A: A higher gear ratio means the wheel turns more times per pedal revolution, so at a fixed cadence the speed rises in proportion to the ratio. Shifting to a smaller cog or a larger chainring is how cyclists raise speed at the same cadence without changing wheel size.
Q: What gear ratio do I need for 25 mph on a road bike?
A: On a 700c rim with a 28 mm tyre, 25 mph requires a cadence of about 107 RPM in a 50x17 gear or about 88 RPM in a 52x15 gear. The exact cadence depends on rim diameter and tire thickness, so use the calculator to match the ratio to a cadence you can hold for the race distance.
Q: How accurate is a bike speed calculator?
A: The math is exact for the cadence, gear, and wheel size you enter, so the speed values are precise to 0.1 mph and 0.1 km/h. Real rides vary with terrain, wind, and tire pressure, so use the result as a flat-road benchmark rather than a race-day prediction.