1. I assume that you want to calculate the value of a force, right?

2. Forces are measured in N (Newton). kg is the unit for a mass. The weight (force!) of a mass of 1 kg is nearly 9.81 N (on Earth).

3. A force of 1 lb correspond to a force of 4.448222 N

4. the area of

5. Your formula becomes:

6. Since you measure the radius in mm the resultant dimenson of your formula is N.