When converting lumber sizes the nominal dimensions (2x) or (4x) should NOT be converted, rather the actual sizes like 1.5″x3.5″ should be soft converted to 38x89mm.
2×4 = 38x89mm
2×6 = 38x140mm
2×8 = 38x184mm
2×10 = 38x235mm
2×12 = 38x286mm
Soft vs. Hard conversion – soft conversion is simply converting inch-pound units to the nearest equivalent metric unit. Panel products for example are typically 4’x8′ which would convert to 1220x2440mm. Hard conversion is when the metric units are rounded to a rational unit. In the preceding example hard conversion for panels would be 1200×2400.
To convert from board feet to cubic meters; according to ASTM E380, multiply board feet by 0.002359737.
See eCourse MAT 120 Metric and Wood for more information.