Calculating Yields

[tau zi]

I am trying to calculate the yield for my items.

The calculation is (Width x Length of belt)/.65)/144

My problem is that when i receive an order the width is in millimeters for example (37mm) but for my calculation i need it to be in Inches (for example 3.7 centimeters) how do i set up a calculation which will always convert the width from millimeters into inches and then carry out the remaining calculation?

[comment]

Try =

Width / 254 * Length / ( .65 * 144 )

or =

Width * Length / 23774.4

This is assuming that Length is already in inches.