m = mass of the falling object g = the acceleration due to gravity. On Earth this is approximately 9. 8 meters per second squared. ρ = the density of the fluid the object is falling through. A = the projected area of the object. This means the area of the object if you projected it onto a plane that was perpendicular to the direction the object is moving. C = the drag coefficient. This number depends on the shape of the object. The more streamlined the shape, the lower the coefficient. You can look up some approximate drag coefficients[2] X Research source .
If you are using the imperial system, remember that pounds is not actually a unit of mass, but of force. The unit of mass in the imperial system is the pound-mass (lbm), which under the gravitational force on the surface of the earth would experience a force of 32 pound-force (lbf). For example, if a person weighs 160 pounds on earth, that person is actually feeling 160 lbf, but their mass is 5 lbm.
In the imperial system, this is the lbf of the object, the number that is commonly called weight. It is more properly the mass in lbm times 32 feet per second squared. In the metric system, the force is the mass in grams times 9. 8 meters per second squared.
As a rough guide, the density of air at sea level when the temperature is 15 °C is 1. 225 kg/m3.
