Cycling Speed Calculator

About the Cycling Speed Calculator

How fast a bike goes comes down to two things you can work out in advance. Mechanically, speed is set by the gear you are in and how fast you turn the pedals — your cadence. Physically, it is set by the power you produce against air resistance, rolling resistance and gravity. Knowing either lets you plan gearing for a hilly event, choose a cassette, check a bike computer, or see what a power target will mean on the road.

This cycling speed calculator does both. In gear and cadence mode it gives the speed for any chainring, rear cog, tyre size and cadence, with the gear ratio, the distance per pedal turn and gear inches, plus the speed at other cadences. In power mode it finds the speed a given number of watts will give for your weight, gradient, riding position and road surface. Both modes show ride times for common distances.

How to Use the Cycling Speed Calculator

Choose From gear and cadence or From power.

For gears, enter the chainring and rear cog teeth, the cadence in rpm, and choose the tyre size, or enter a measured wheel circumference.

For power, enter the power in watts, the rider and bike weights, the gradient, and choose the riding position and road surface.

The Formula

  gear ratio         = chainring teeth ÷ cog teeth
  distance per turn  = gear ratio × wheel circumference
  speed (km/h)       = distance per turn (m) × cadence × 60 ÷ 1,000
  gear inches        = gear ratio × wheel diameter in inches

In power mode, the calculator uses the same physics as the cycling power calculator — power = (gravity + rolling + air resistance) × speed ÷ (1 − drivetrain loss) — and searches for the speed at which the required power equals yours.

Step-by-Step Example

A 50×17 gear on 700 × 25c tyres (2,105 mm circumference) at 90 rpm:

  gear ratio         50 ÷ 17 = 2.94
  distance per turn  2.94 × 2.105 m = 6.19 m
  speed              6.19 × 90 × 60 ÷ 1,000 = 33.4 km/h (20.8 mph)
  gear inches        2.94 × 26.4 in = 77.6

At other cadences the same gear gives 22.3 km/h at 60 rpm, 29.7 at 80, 37.1 at 100 and 40.9 at 110.

From power: a 75 kg rider on a 9 kg bike, on the hoods on an average flat road, producing 200 watts, rides at about 33.4 km/h. At 180 W the speed is about 32.0 km/h and at 220 W about 34.6 km/h — 10 percent more power buys only about 4 percent more speed.

Speed Chart at 90 rpm

On 700 × 25c tyres at 90 rpm:

  Gear     Speed         Gear     Speed
  50×11    51.7 km/h     34×11    35.1 km/h
  50×13    43.7 km/h     34×17    22.7 km/h
  50×15    37.9 km/h     34×21    18.4 km/h
  50×17    33.4 km/h     34×25    15.5 km/h
  50×19    29.9 km/h     34×28    13.8 km/h
  50×21    27.1 km/h     34×32    12.1 km/h
  50×25    22.7 km/h
  50×28    20.3 km/h

Notice that 50×25 and 34×17 give the same speed: both have a ratio of 2.0. Many gear combinations overlap, which is why a double chainset with an 11-speed cassette has fewer truly different gears than its 22 combinations suggest.

Wheel Size and Circumference

The wheel's rolling circumference is the distance it travels in one turn, including the tyre. Standard values from bike-computer setup tables are 2,096 mm for 700 × 23c, 2,105 mm for 700 × 25c, 2,136 mm for 700 × 28c, 2,155 mm for 700 × 32c and 2,068 mm for a 26 × 2.1 in mountain bike tyre. For the best accuracy, mark the tyre, roll the bike one full turn with your weight on it, and measure the distance in millimetres.

Gear Inches and Development

Gear inches is an old measure that describes a gear as the diameter of the wheel on a penny-farthing that would travel the same distance per pedal turn. A 50×17 on a road bike is about 78 gear inches. Development, or metres of development, is the modern metric equivalent: the distance the bike travels per pedal turn, 6.19 metres in the same gear. Both let you compare gears across different wheel sizes.

Choosing Gears for Climbs

For steep hills, the lowest gear matters more than the highest. A 34×28 at 80 rpm gives about 12.4 km/h on 700 × 28c tyres; at the same effort on a 10 percent climb, many riders would be going slower still. If you find yourself grinding at 50 or 60 rpm on your local climbs, a larger rear cog or smaller chainring will let you spin at a more sustainable cadence. In power mode, 250 W on a 6 percent climb gives about 15.3 km/h for the example rider — compared with about 37 km/h on the flat in the drops.

Understanding Your Result

The headline is the speed in km/h and mph.

The gear line gives the ratio, distance per pedal turn and gear inches — or, in power mode, your watts per kilogram.

The other cadences or other powers line shows how the speed changes.

The ride times line gives times for 20 km, 40 km, 100 km and 100 miles at this speed.

When Should You Use This Calculator?

Use it to choose a chainset and cassette for a hilly sportive or tour.

Use it to check what cadence a target speed needs in a given gear.

Use it to estimate the speed a power target will give on the flat or on a climb.

Use it to compare gear ratios between bikes with different wheel sizes.

Common Mistakes

Using the rim size instead of the rolling circumference. The tyre adds to the size.

Assuming more gears means a wider range. Many combinations overlap.

Expecting speed to rise with power one for one. Air resistance makes it much slower.

Choosing gears for the flat. It is the steepest climb that decides the lowest gear.