I am currently into estimating job for a small construction company. In my previous experiences, in calculating the labor cost for a certain job,

Labor cost = material cost * 0.45

I did this to simplify the computation. Are there specific labor factor for different job classification, e.g. concreting, masonry, carpentry, painting, steel, rebars, etc. that I can adopt?

Note: This will not involve equipment in the process.