Estimates the maximum rate at which the body takes in oxygen, from how far you can run in 12 minutes: (distance − 504.9) ÷ 44.73. It is the standard measure of endurance. The distance has to exceed 505 m.
VO2 max is the greatest rate at which the body can take in oxygen, and it is the standard measure of endurance. The Cooper test estimates it from how far you can run in 12 minutes.
is the distance in metres. The units are mL/kg/min: millilitres of oxygen per kilogram of body weight per minute.
One MET is defined as an oxygen uptake of 3.5 mL/kg/min, the rate at rest. Dividing VO2 max by 3.5 gives the intensity in METs that a person can sustain at their limit. Ordinary walking is about 3 METs and jogging about 7.
Someone weighing 65 kg covers 2400 m in 12 minutes. That gives mL/kg/min. Across the whole body that is 2.75 litres of oxygen a minute, or 12.1 METs.
The kilogram in the units is there because the figure is per kilogram of body mass. A larger body takes in more oxygen in total, but it also has more of itself to carry. For comparing what people can actually do, the figure per kilogram is the fairer one.
The formula holds only above 504.9 m, which is slower than walking pace and outside the range it was built for.