Convert your lumber measure to the metric system.
In the United States, board feet (BF) is used. Calculate your CBM from BF using a conversion factor. Because a board foot is so much smaller than a CBM, the calculation is usually done from a thousand board feet (MBF) to CBM. Thus, it is best to first convert your lumber measurement from BF to MBF, and calculate the CBM from there.
Take your measurement in BF and divide it by 1,000 to get MBF. For example, if your measurement is 12,000 BF, you would have 12 MBF.
Multiply your MBF by 2.36 to get the amount in CBM. In this example, 12 MBF equals 28.32 CBM.
Calculate CBM from MBF quickly by multiplying CBM by 0.4238, so 10 CBM is 4.238 MBF.