Average cycling speed

No set answer, depends on bicycle, terrain and rider. Can be anything between 2-100 MPH. Most people do between 10-20 MPH.
The average speed of a bicycle is between 11 and 31 miles per hour. A speed distance time calculator can provide a more accurate speed of how fast an individual rides on their bicycle.
All depends on how fast they pedal and what kind of a bike they're on.

When I ride with my family ... about 10 mph

When I ride solo on my road bike ... about 17 mph

In today's stage of the Tour de France, the average rider was expected to (during the last 26 km) average about 80kmh, or 49+ mph.

Depends on how you categorize riding. There has been aerodynamic recumbent bikes on the flat roads that have clocked 82mph which is the current fastest top speed from last I checked (set in 2002).

Downhill on road bicycles has reached to a little bit above 65mph downhill motorpacing I've seen exceed 100mpg.

Then there has also been motor pacing techniques to test a cyclists speed which a pro can do that at around 100mph or so. however The fastest speed achieved on a bicycle was 204.73 kph (127.243 mph), by Jose Meiffret (France), July 16, 1962, on the German Autobahn from Freiburg, behind a car (see below Events).

-http://hypertextbook.com/facts/2001/AileenChou.shtml
13-15 mph EDIT: That converts to 20-24 Kilometres per hour or about 20 feet per second.
Depends who the Bicycle rider is. Top professional riders will average 50 Km/hr and more. Good bike riders 40 km/hr and some one who is riding a standard commuter bike riding to work might average 20 km/hr on a good day.
Really hard to tell. Me, on easy roads - 20 MPH. Racer, on easy roads - 25 MPH. Casual rider on easy road - 10-15 MPH.
I think about 16-18 km/h
That's about as silly as asking how fast a car goes. A bike can be ridden at a walking pace, but can also reach 50 MPH or more during a descent.

Depends partly on your bike, partly on your ability and ambition.

If you maintain a cadence (pedaling pace) of 70 rpm on a bike giving 77 gear inches you get a speed of 12.1 miles per hour.

You can easily determine your own speed using the following formula:

((((((T1/T2)D)3.1416)C)60)/12)/5280 = miles per hour

Where:

T1=number of teeth on the chainring (attached to the pedals)

T2=number of teeth on the cluster ring (attached to the rear wheel)

D=diameter in inches of the rear wheel (usually imprinted on the tire)

3.1416 = pi

C=your cadence - the number of revolutions per minute of the pedals

60=multiplier to change minutes to hours

12=divisor to change inches to feet

5280=divisor to change feet to miles

T1/T2 is the ratio of your gears - count teeth on the rings you are actually using

Multiplying this ratio times the wheel diameter in inches gives you your GEAR in inches. GEAR is the diameter of the virtual drive wheel created by your gear system.

Multiplying GEAR by pi gives you circumference of the virtual drive wheel.

Multiplying this circumference times your cadence gives you inches traveled per minute.

The other numbers convert the result to miles per hour.

Real-world number vary considerably. I can do about 18-20 MPH for hours under road conditions, racers can do 25-30 mph. A frequently given number for casual riding is about 10 mph.

The average person rides a bike between 12 and 19 kph. This is highly dependent on the type of bike being ridden, as standard 26" wheel mountain bikes are considerably slower then road bikes.
With a good bike, a fairly average person can hit about 40 KMH / 25 MPH for a short period, and cover a tad more than 30 km /20 miles in one hour.