What is the speed of brisk walk?

According to http://wiki.answers.com/Q/How_many_miles_per_hour_constitutes_a_brisk_walk

Walking 4 mph is considered to be brisk.

1 mile = 1.609344 kilometers

4 mph = 4 x 1.609344 km/h
= 6.437376 km/h
= 4 x 1.609344 x 1000/60/60 meters per second
= 1.78816 meters per second

Therefore, the speed of brisk walk is 4 mph or 6.437376 km/h or 1.78816 meters per second.